Sam can mow a lawn in 40 minutes. Melissa can mow the same lawn in 80 minutes. How long does it take for both Sam and Melissa to mow the lawn if they are working together?
Answer:
It will take them both 24 minutes to mow the lawn if they are working together.
Step-by-step explanation:
Given that Sam can mow a lawn in 40 minutes, and Melissa can mow the same lawn in 80 minutes, to determine how long does it take for both Sam and Melissa to mow the lawn if they are working together, the following calculation must be performed:
1/40 + 1/60 = 1 / X
3X + 2X = 120
X = 120/5
X = 24
Thus, it will take them both 24 minutes to mow the lawn if they are working together.
Find all the zeros of f(x).
f(x) = 2x3 + 7x2 - 28x + 12
Arrange your answers from smallest to largest. If
there is a double root, list it twice.
Plz help!
Answer:
The zeroes are -6, 1/2 and 2.
Step-by-step explanation:
f(x) = 2x3 + 7x2 - 28x + 12 = 0
From the first and last coefficient 2 and 12, one guess for a zero is x = 2.
So substituting x = 2:
f(2) = 16+ 28 - 56 + 12 = 0
So x = 2 is a zero and x - 2 is a factor of f(x)
Performing long division:
x - 2)2x3 + 7x2 - 28x + 12( 2x2 + 11x - 6 <------- Quotient
2x3 - 4x2
11x2 - 28x
11x2 - 22x
- 6x + 12
-6x + 12
.............
Now we solve
2x2 + 11x - 6 = 0
(2x - 1)(x + 6) = 0
2x - 1 = 0 or x + 6 = 0, so:
x = 1/2, x = -6.
Answer: -6, 1/2, 2.
Step-by-step explanation:
{(x) = 2x3 + 7x2 - 28x + 12 = 0
From the first and last coefficient 2 and 12, one
guess for a zero is x=2.
So substituting x=2:
{(2) = 16+ 28 - 56 + 12 = 0
So x = 2 is a zero and x - 2 is a factor of f(x)
Performing long division:
X - 2)2x3 + 7x2 - 28x + 12(2x2 + 11x - 6 <
Quotient
Find the missing side. Round your answer to the nearest tenth
Answer:
x = 24.8
Step-by-step explanation:
Since this is a right triangle, we can use trig functions
Sin theta = opp / hypotenuse
sin 75 = 24 /x
x sin 75 = 24
x = 24/ sin 75
x=24.84662
Rounding to the nearest tenth
x = 24.8
state the hundred thousands place for 7,832,906,215
Answer:
Step-by-step explanation:
6 is the thousands place
0 (right next to it) is the 10 thousands place
9 is the hundred thousands place. There is only 1 nine present so the answer is unique.
what is the image of ( 4, -8 ) after a dilation by a scale factor of 1/4 centered at the origin ?
what we know?:
* scale factor of 1/4
* the point (4, -8)
all we have to do is put 4/4 (because we are dilating by 1/4)
4/4= 1
same for the other one: -8/4= -2
FINAL ANSWER: (1, -2)
Does anyone know how to take the fuzzy stuff off
Answer:
???
Step-by-step explanation:
• The difference between a polynomial or rational equation and polynomial or rational inequality
Answer:
An equation has an equal sign between two expressions, while an inequality has a ≤ or ≥ sign.
Given limit f(x) = 4 as x approaches 0. What is limit 1/4[f(x)]^4 as x approaches 0?
Answer:
[tex]\displaystyle 64[/tex]
General Formulas and Concepts:
Calculus
Limits
Limit Rule [Variable Direct Substitution]: [tex]\displaystyle \lim_{x \to c} x = c[/tex]
Limit Rule [Variable Direct Substitution Exponential]: [tex]\displaystyle \lim_{x \to c} x^n = c^n[/tex]
Limit Property [Multiplied Constant]: [tex]\displaystyle \lim_{x \to c} bf(x) = b \lim_{x \to c} f(x)[/tex]
Step-by-step explanation:
Step 1: Define
Identify
[tex]\displaystyle \lim_{x \to 0} f(x) = 4[/tex]
Step 2: Solve
Rewrite [Limit Property - Multiplied Constant]: [tex]\displaystyle \lim_{x \to 0} \frac{1}{4}[f(x)]^4 = \frac{1}{4} \lim_{x \to 0} [f(x)]^4[/tex]Evaluate limit [Limit Rule - Variable Direct Substitution Exponential]: [tex]\displaystyle \lim_{x \to 0} \frac{1}{4}[f(x)]^4 = \frac{1}{4}(4^4)[/tex]Simplify: [tex]\displaystyle \lim_{x \to 0} \frac{1}{4}[f(x)]^4 = 64[/tex]Topic: AP Calculus AB/BC (Calculus I/I + II)
Unit: Limits
Book: College Calculus 10e
Answer: C. 64
Step-by-step explanation:
Edge 100%
Find the area of a rectangle whose length is 14cm and breadth is 6cm
Answer:
Ellos dan las pistas de algunos problemas se pueden resolver de forma automática, los valores numéricos tienen ninguna importancia en los distintos ejemplos.
Traza 1
Uno de los lados de un rectángulo es 20 cm de largo; un segundo lado del rectángulo es de 0,85 m de largo. Calcular el perímetro y el área del rectángulo.
Traza 2
Calcular el área de un rectángulo cuyas dimensiones son 85 cm de largo y 20 cm respectivamente.
Traza 3
La base de un rectángulo es 20 cm de largo; la área es de 300 cm². Calcular la altura del rectángulo.
Traza 4
La altura de un rectángulo es 15 cm de largo; la área es de 300 cm². Calcula la base del rectángulo.
Traza 5
Un rectángulo tiene la altura que es de 3/8 de la base; la suma de las longitudes de los dos segmentos es 44 cm. Determinar el área del rectángulo y el perímetro.
Traza 6
La base de un rectángulo es de 0,40 m de largo; La altura del rectángulo es 30 cm. Calcular la diagonal.
Traza 7
Un tamaño de un rectángulo es un medio del lado de un cuadrado que tiene el perímetro de 20 cm. Sabiendo que los dos polígonos tienen el mismo perímetro, calcula la medida del tamaño del rectángulo.
Traza 8
La diagonal de un rectángulo es de 50 cm; la base es de 3/4 de la altura. Calcular el perímetro y el área del rectángulo.
Traza 9
La diagonal de un rectángulo mide 50 cm; ella es 5/3 de altura. Calcular el perímetro y el área del rectángulo.
Traza 10
Una mesa rectangular tiene lados de 180 cm y 90 cm respectivamente. Cuál es el perímetro y el área de un mantel que cuelga de 20 cm alrededor de la mesa?
Traza 11
Calcular el área de un rectángulo que tiene la altura 10 cm de largo, sabiendo que la medida de la base es el doble de la altura.
Traza 12
La diferencia entre el tamaño de un rectángulo es 12 cm y una es el triple de la otra. Calcular el área del rectángulo
Traza 13
La suma entre el tamaño de un rectángulo es 12 cm y una es el triple de la otra. Calcular el área del rectángulo
Traza 14
La suma de la base y la altura de un rectángulo es 50 cm; la base es superior a la altura de 4 cm. Calcular el área del rectángulo.
Traza 15
El semi-perímetro de un rectángulo es 32 cm y una dimensión es de 3/5 de la otra. Calcular el área del rectángulo.
Traza 16
El semi-perímetro de un rectángulo es 30 cm y una dimensión es igual a los sus 2/5. Calcular el área del rectángulo.
Traza 17
Un rectángulo tiene una base de 20 cm y una altura igual a 2/5 de la base. Calcular el perímetro y el área del rectángulo.
Traza 18
Un rectángulo tiene el área de 600 cm² y la base es 20 cm de largo. Cuál es su perímetro ?
Traza 19
Un rectángulo tiene un perímetro de 100 cm y la base es 30 cm de largo. Calcula su área.
Traza 20
Un rectángulo tiene un perímetro de 120 cm. Sabiendo que un tamaño es tres veces la otra, calcula el área del rectángulo.
Traza 21
La diferencia entre el tamaño de un rectángulo es 10 dm. Sabiendo que el perímetro es 100 dm, calcula el área del rectángulo.
Traza 22
Un rectángulo tiene un perímetro de 100 cm. Calcula su área sabiendo que la medida de la base es superior a la de la altura de 10 cm.
Traza 23
En el perímetro de un rectángulo es de 100 cm y la altura es de 20 cm de largo. Calcular el perímetro de un rectángulo equivalente a el mismo y que tiene su base de 40 cm de largo.
Traza 24
Un rectángulo es formado por dos cuadrados congruentes que tienen cada uno el perímetro de 24 cm. Calcular el perímetro y el área del rectángulo.
Traza 25
Un rectángulo es formado por tres cuadrados congruentes con cada lado 20 cm de largo. Calcular el perímetro y el área del rectángulo.
Traza 26
Un rectángulo es formado por dos cuadrados congruentes. Sabiendo que el perímetro del rectángulo es de 180 cm, calcular su área.
Traza 27
Un rectángulo y un cuadrado tienen el mismo perímetro. El lado de un cuadrado de 45 cm y las dimensiones del rectángulo son una 1/2 de la otra. Calcular el área del rectángulo.
Traza 28
Dos rectángulos son equivalentes. Sabiendo que las dimensiones de el primero miden respectivamente 30 cm y 20 cm, y que la base del segundo rectángulo es 40 cm de largo, calcula la diferencia entre los dos perímetros.
Traza 29
Calcular el perímetro de la figura y el área de la parte interior con la obtención de las medidas a partir del dibujo:
Traza 30
Calcular el perímetro de la figura y el área de la parte interior con la obtención de las medidas a partir del dibujo:
Traza 31
Un constructor ha comprado un terreno que tiene la planta mostrada en el dibujo y las dimensiones en metros se indican en la figura. Calcula el área y el perímetro de la tierra.
Traza 32
Una parcela de tierra tiene una forma rectangular con unas dimensiones de 50 m y de 30 m de largo. En el interior se ha construido una casa que ocupa una superficie rectangular de longitud 20 m y de 8 m de ancho. Calcular el área de la tierra permanecida libre.
Traza 33
Step-by-step explanation:
Answer:
A= 84cm
Step-by-step explanation:
length x width= area
plug in the given information.
14cm x 6cm = A
A=84
with a length of 14cm and a width of 6cm multiply them for an area of 84cm.
Does this graph represent a function?
Answer:
I think it's a function
Step-by-step explanation:
as you can see in the picture curve drawn in a graph represents a function, if every vertical line intersects the curve in at most one point. So I think its a function.
Answer:
yes
Step-by-step explanation:
it's a cubic function having maximum and minimum turning points
it has a point of inflation, y - intercept and x-intercept
What is the length of segment AC?
Answer:
10 units
Step-by-step explanation:
Point A (3,-1)
Point B (-5,5)
Distance between them,
√{(-5-3)²+(5-(-1))²}
= √{(-8)²+6²}
= √(64+36)
= √100
= 10 units
Kezang was 5 times as old as his son 10 years ago. After 8 years, Kezang will be twice as
old as his son. What are their present age
!!! HELP ASAP !!! I almost got the problem but the problem was the rounding. I believe I rounded right but it is still incorrect. Can someone please help me on the rounding portion of the question? Thank you for your help!!!
Male bluethroats have a complex song which is thought to be used to attract female birds. Let x denote the duration of a randomly selected song (in seconds) from a male bluethroat. The authors of research on bluethroat song report the mean song duration is 13.8 seconds and the standard deviation of song durations is 11.8 seconds. The authors also noted that the song length distribution is not normal.
Required:
a. Let = average song duration (in seconds) for a sample of 36 male bluethroat songs. Is this distribution of the sample mean song duration " normally distributed" ?
b. Find the probability that a sample of 36 male bluethroat songs will have a mean duration greater than 12 seconds. Draw, label, and shade a graph to illustrate your result.
Answer:
a) Sample size larger than 30, so by the Central Limit Theorem, yes.
b) 0.8199 = 81.99% probability that a sample of 36 male bluethroat songs will have a mean duration greater than 12 seconds. The sketch is given at the end.
Step-by-step explanation:
To solve this question, we need to understand the normal probability distribution and the central limit theorem.
Normal Probability Distribution
Problems of normal distributions can be solved using the z-score formula.
In a set with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the z-score of a measure X is given by:
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
The Z-score measures how many standard deviations the measure is from the mean. After finding the Z-score, we look at the z-score table and find the p-value associated with this z-score. This p-value is the probability that the value of the measure is smaller than X, that is, the percentile of X. Subtracting 1 by the p-value, we get the probability that the value of the measure is greater than X.
Central Limit Theorem
The Central Limit Theorem establishes that, for a normally distributed random variable X, with mean [tex]\mu[/tex] and standard deviation [tex]\sigma[/tex], the sampling distribution of the sample means with size n can be approximated to a normal distribution with mean [tex]\mu[/tex] and standard deviation [tex]s = \frac{\sigma}{\sqrt{n}}[/tex].
For a skewed variable, the Central Limit Theorem can also be applied, as long as n is at least 30.
Mean song duration is 13.8 seconds and the standard deviation of song durations is 11.8 seconds.
This means that [tex]\mu = 13.8, \sigma = 11.8[/tex]
Sample of 36
This means that [tex]n = 36, s = \frac{11.8}{\sqrt{36}} = 1.9667[/tex]
a. Let = average song duration (in seconds) for a sample of 36 male bluethroat songs. Is this distribution of the sample mean song duration " normally distributed" ?
Sample size larger than 30, so by the Central Limit Theorem, yes.
b. Find the probability that a sample of 36 male bluethroat songs will have a mean duration greater than 12 seconds. Draw, label, and shade a graph to illustrate your result.
This is 1 subtracted by the p-value of Z when X = 12. So
[tex]Z = \frac{X - \mu}{\sigma}[/tex]
By the Central Limit Theorem
[tex]Z = \frac{X - \mu}{s}[/tex]
[tex]Z = \frac{12 - 13.8}{1.9667}[/tex]
[tex]Z = -0.915[/tex]
[tex]Z = -0.915[/tex] has a p-value of 0.1801.
1 - 0.1801 = 0.8199
0.8199 = 81.99% probability that a sample of 36 male bluethroat songs will have a mean duration greater than 12 seconds.
Sketch:
1. Define the following: Odds ratio Relative risk 2. Describe how to calculate the Odds ratio and provde the formula. 3. Describe how to calculate the Relative Risk and provide the formula.
Answer and Explanation:
Odds ratio is the odds that an outcome would happen given a level of exposure in comparison to the occurrence of that outcome without exposure. Odds ratio is calculated by dividing odds of event occurring with exposure(the first group) by odds of event(usually disease) occurring without exposure. Odds is different from probability(denoted p/1-p). While probability is the number of favorable events divided by total number of events, odds is number of favorable events/number of unfavorable events.
Relative risk, also measuring relationship between exposure and outcome, is the ratio of the probability that an outcome would occur without exposure and probability that an outcome would occur with exposure.
38)
A man completes a job in 5 days working 8 hours a day. How many days will he take to complete the same job working 2 hours overtime per day in addition?
Answer:
dbcjchdiskcnbcksksnnckdkxnn
Assume the random variable X has a binomial distribution with the given probability of obtaining a success. Find the following probability, given the number of trials and the probability of obtaining a success. P(X > 3), n = 5, p = 0.2
Answer:
0.0064
0.00032
Step-by-step explanation:
Given the details:
P(X > 3), n = 5, p = 0.2
The binomial distribution is related using the formula:
P(x = x) = nCx * p^x * q^(n-x)
q = 1 - p = 1 - 0.2 = 0.8
P(X > 3) = p(x = 4) + p(x = 5)
P(x = 4) = 5C4 * 0.2^4 * 0.8^1 = 5 * 0.2^4 * 0.8^1 = 0.0064
P(x = 5) = 5C5 * 0.2^5 * 0.8^0 = 1 * 0.2^5 * 0.8^0 = 0.00032
Is the following shape a square? How do you know?
.8
C.
A
0
O A. No, the opposite sides are not parallel.
B. Yes, the opposite sides are parallel, and all sides are the same
length
O C. No, the sides are not congruent.
D. Yes, the adjacent sides are perpendicular, and all sides are the
same length
PLEASEEEE HELPPPPPPP!!!!!
To find S or T add them together:
3/5 + 1/3
Rewrite the fractions to have a common denominator
9/15 + 5/15 = 14/15
Answer: 14/15
Step-by-step explanation:
Here is your answer . Hope it helps.
Omar keeps his sneaker collection carefully arranged on the floor of his closet. 8 pairs of
sneakers fit perfectly side-by-side from one end of the closet to the other. The closet is 60
inches wide.
How wide is each pair of sneakers?
Answer:
7.5 inches wide. I wasnt wrong. for a second i thought it was asking for the width of each individual sneaker.
Answer:
each pair of sneakers are 7.5 inches wide
PLEASE ANSWER!!
What is the remainder for the synthetic division problem below?
2/ 3 1 2 -7
A. 25
B. 17
C. -29
D. -39
A: 25.
Explanation: Check the attached image.
For synthetic division, you just need to multiply the 1st number of the polynomial by the divisior, and then, add it up to the next number; then, the coefficient will be multiplied by the divisor, and so on and so forth until you reach the last number... that last coefficient at the end is the reminder that you've been asked for
Evaluate the following expressions using the chip method. SHOW ALL WORK!!!
Answer:
a. -7 b. -20c. 7Step-by-step explanation:
a. -9+2, in this case, it is -7 because you take the bigger number and subtract it by the lower number. If the bigger number is negative your answer will be negative, if the bigger number is positive it will be positive it is just really a basic subtraction problem just add the sign.b. In multiplication +++=+ ++-=- and a -+-=+ do your problem without thinking about the signs and then add the signs with the formula I showed you.c. ---=+Hope this helps :)!
If the number of observations for each sample is 150 units, what is the 3-sigma upper control limit of the process
Complete Question
Complete Question is attached below
Answer:
[tex]UCL= 0.25[/tex]
Step-by-step explanation:
From the question we are told that:
Sample size[tex]n=150[/tex]
Sample Variants [tex]s=7[/tex]
Sigma control limits [tex]Z = 3[/tex]
Therefore
Total number of observations is Given as
[tex]T_o=n*s[/tex]
[tex]T_o=150 *7[/tex]
[tex]T_0=1050[/tex]
Generally
Summation of defectivee
[tex]\sum np=23+34+15+30+25+22+18[/tex]
[tex]\sum np= 167[/tex]
Generally the equation for P-bar is mathematically given by
[tex]P-bar=\frac{\sum np}{T_o}[/tex]
[tex]P-bar=\frac{167}{1050}[/tex]
[tex]P-bar=0.16[/tex]
Therefore
[tex]Sp=\sqrt{\frac{P-bar(1-P-bar)]}{ n}}[/tex]
[tex]Sp=\sqrt{\frac{[0.159(1-0.159)]}{150}}[/tex]
[tex]Sp=0.03[/tex]
Generally the equation for 3-sigma upper control limit of the process is mathematically given by
[tex]UCL = P-bar + Z*Sp[/tex]
[tex]UCL= 0.16 + 3*0.03[/tex]
[tex]UCL= 0.25[/tex]
Two buses leave towns 576 kilometers apart at the same time and travel toward each other. One bus travels 12
h
slower than the other. If they meet in 3 hours, what is the rate of each bus?
km
Rate of the slower bus:
Rate of the faster bus:
Answer:
Rate of slower bus; 90 km/h
Rate of faster bus; 102 km/b
Step-by-step explanation:
We know that formula do distance is;
Distance = speed/time
We are told that One bus travels 12h slower than the other.
Let speed of slower bus be x.
Thus;
Speed of faster bus = x + 12
Speed of slower bus = x
After 3 hours, distance by faster bus = 3(x + 12)
Speed of slower bus = 3x
Since the towns are 576 km apart, then;
3(x + 12) + 3x = 576
Divide through by 3 to get;
x + 12 + x = 192
2x + 12 = 192
2x = 192 - 12
2x = 180
x = 180/2
x = 90 km/h
Faster bus speed = 90 + 12 = 102 km/h
B
15x+7
6x+2y|
y +3
2y + 1
С
E
The triangles are congruent. Find the length of each hypotenuse.
A. 3
B. 5
C 17
Answer:
Hypothenus = 22
Step-by-step explanation:
From the question given above, we were told that the triangles are congruent (i.e same size). Thus,
AC = EF
BC = DE
To obtain the length of each Hypothenus, we shall determine the value of y and x. This can be obtained as follow:
For y:
AC = y + 3
EF = 2y + 1
AC = EF
y + 3 = 2y + 1
Collect like terms
3 – 1 = 2y – y
2 = y
y = 2
For x:
BC = 5x + 7
DE = 6x + 2y
y = 2
DE = 6x + 2(2)
DE = 6x + 4
BC = DE
5x + 7 = 6x + 4
Collect like terms
7 – 4 = 6x – 5x
3 = x
x = 3
Finally, we shall determine the length of each Hypothenus. This can be obtained as follow:
Hypothenus = BC
Hypothenus = 5x + 7
x = 3
Hypothenus = 5x + 7
Hypothenus = 5(3) + 7
Hypothenus = 15 + 7
Hypothenus = 22
OR
Hypothenus = DE
DE = 6x + 2y
y = 2
x = 3
Hypothenus = 6(3) + 2(2)
Hypothenus = 18 + 4
Hypothenus = 22
A psychologist suspects that heroin addicts have a different assessment of self-worth than others in the general population. On a test designed to measure self-worth, the mean for the general population is 48.6. The psychologist obtains a random sample of 40 test scores produced by heroin addicts and found the sample mean and the sample standard deviations are 45.5 and 8.5, respectively. Do these data indicate the self-worth of heroin addicts is less than that of the general population?
Answer:
The p-value of the test if 0.0131, which is less than the standard significance level of 0.05, meaning that these data indicates that the self-worth of heroin addicts is less than that of the general population.
Step-by-step explanation:
On a test designed to measure self-worth, the mean for the general population is 48.6.
At the null hypothesis, we test if the mean is of 48.6, that is:
[tex]H_0: \mu = 48.6[/tex]
A psychologist suspects that heroin addicts have a different assessment of self-worth than others in the general population. Test if it is lower.
At the alternative hypothesis, we test if the mean is lower, that is:
[tex]H_1: \mu < 48.6[/tex]
The test statistic is:
We have the standard deviation for the sample, which means that the t-distribution is used to solve this question.
[tex]t = \frac{X - \mu}{\frac{s}{\sqrt{n}}}[/tex]
In which X is the sample mean, [tex]\mu[/tex] is the value tested at the null hypothesis, s is the standard deviation and n is the size of the sample.
48.6 is tested at the null hypothesis:
This means that [tex]\mu = 48.6[/tex]
The psychologist obtains a random sample of 40 test scores produced by heroin addicts and found the sample mean and the sample standard deviations are 45.5 and 8.5, respectively.
This means that [tex]n = 40, X = 45.5, s = 8.5[/tex]
Value of the test statistic:
[tex]t = \frac{X - \mu}{\frac{s}{\sqrt{n}}}[/tex]
[tex]t = \frac{45.5 - 48.6}{\frac{8.5}{\sqrt{40}}}[/tex]
[tex]t = -2.31[/tex]
P-value of the test:
The p-value of the test is a one-tailed test(mean lower than a value), with t = -2.31 and 40 - 1 = 39 df.
Using a t-distribution calculator, this p-value is of 0.0131.
The p-value of the test if 0.0131, which is less than the standard significance level of 0.05, meaning that these data indicates that the self-worth of heroin addicts is less than that of the general population.
Shirley has a collection of 50 stamps and adds 4 stamps daily to her collection. Model this situation as a function of number of days (d).
Answer:
N = 50 +4d
Step-by-step explanation:
Take the original number of stamps and add the stamps per days times the number of days
N = 50 +4d
I need help please. Show work
Answer:
28
Step-by-step explanation:
10/14 mph no wind
20 wind
14 x 2 = 28
28 mph with wind
Uuannsnnsnndn d. DND. D
Answer:
im so confused
Step-by-step explanation:
Answer:
what is this goat saying
find the differential equation of this function and indicate the order y = e^3x (acos3x +bsin3x)
Answer:
y"-6y'+18y=0
Second order
Step-by-step explanation:
Since there are 2 constants, the order of the differential equation will be 2. This means we will need to differentiate twice.
y = e^(3x) (acos3x +bsin3x)
y'=3e^(3x) (acos3x+bsin3x)
+e^(3x) (-3asin3x+3bcos3x)
Simplifying a bit by reordering and regrouping:
y'=e^(3x) cos3x (3a+3b)+e^(3x) sin3x (3b-3a)
y"=
3e^(3x) cos3x (3a+3b)+-3e^(3x) sin(3x) (3a+3b)
+3e^(3x) sin3x (3b-3a)+3e^(3x) cos(3x) (3b-3a)
Simplifying a bit by reordering and regrouping:
y"=
e^(3x) cos3x (9a+9b+9b-9a)
+e^(3x) sin3x (-9a-9b+9b-9a)
Combining like terms:
y"=
e^(3x) cos3x (18b)
+e^(3x) sin3x (-18a)
Let's reorder y like we did y' and y".
y = e^(3x) (acos3x +bsin3x)
y=e^(3x) cos3x (a) + e^(3x) sin3x (b)
Objective is to find a way to combine or combine constant multiples of y, y', and y" so that a and b are not appearing.
Let's start with the highest order derivative and work down
y"=
e^(3x) cos3x (18b)
+e^(3x) sin3x (-18a)
We need to get rid of the 18b and 18a.
This is what we had for y':
y'=e^(3x) cos3x (3a+3b)+e^(3x) sin3x (3b-3a)
Multiplying this by -6 would get rid of the 18b and 18a in y" if we add them.
So we have y"-6y'=
e^(3x) cos3x (-18a)+e^(3x) sin3x (-18b)
Now multiplying
y=e^(3x) cos3x (a) + e^(3x) sin3x (b)
by 18 and then adding that result to the y"-6y' will eliminate the -18a and -18b
y"-6y'+18y=0
Also the characteristic equation is:
r^2-6r+18=0
This can be solved with completing square or quadratic formula.
I will do completing the square:
r^2-6r+18=0
Subtract 9 on both sides:
r^2-6r+9=-9
Factor left side:
(r-3)^2=-9
Take square root of both sides:
r-3=-3i or r-3=3i
Add 3 on both sides for each:
r=3-3i or r=3+3i
This confirms our solution.
Another way to think about the problem:
Any differential equation whose solution winds up in the form y=e^(px) (acos(qx)+bsin(qx)) will be second order and you can go to trying to figure out the quadratic to solve that leads to solution r=p +/- qi
Note: +/- means plus or minus
So we would be looking for a quadratic equation whose solution was r=3 ×/- 3i
Subtracting 3 on both sides gives:
r-3= +/- 3i
Squaring both sides gives:
(r-3)^2=-9
Applying the exponent on the binomial gives:
r^2-6r+9=-9
Adding 9 on both sides gives:
r^2-6r+18=0
