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[tex] (x + 5)(x - 4)(x + 2) = [/tex]
[tex](x + 5) ({x}^{2} - 2x - 8) = [/tex]
[tex] {x}^{3} - 2 {x}^{2} - 8x + 5 {x}^{2} - 10x - 40 = \\ [/tex]
[tex] {x}^{3} + 3 {x}^{2} - 18x - 40[/tex]
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Compare :
[tex] {x}^{3} + 3 {x}^{2} - 18x - 40[/tex]
[tex] {x}^{3} + a {x}^{2} - 18x + b[/tex]
Thus :
[tex]a = 3[/tex]
and
[tex]b = - 40[/tex]
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