Question

F(x)=-9x^2-2x and g(x)=3x^2+6x-9, find (f-g)(x) and (f-g)(-4)

Answer 1

`(f-g)(x) = -12x^(2) - 8x + 9`

(f-g)(-4) = -151

Explanation:

To find f-g(x) we subtract the common terms. So

`f(x) = -9x^(2) - 2x`

`g(x) = 3x^(2) + 6x - 9`

(f-g)(x)

`(f-g)(x) = f(x) - g(x) = -9x^(2) - 2x - (3x^(2) + 6x - 9) = -9x^(2) - 2x - 3x^(2) - 6x + 9 = (-9 - 3)x^(2) + (-2 - 6)x + 9 = -12x^(2) - 8x + 9`

(f-g)(-4)

`(f-g)(x) = -12x^(2) - 8x + 9`

We replace x by -4

`(f-g)(-4) = -12(-4)^(2) - 8(4) + 9= -151`

(f-g)(-4) = -151