Question

With the functions: f(x) = x^2 + 3x and g(x) = -3 + x what is f(g(x)) ?

Can anyone help with this? I keep getting x^2 + 3x - 9 but that isn't one of the options.

The choices are:
a. x^2 - 3x
b. x^2 - 3x + 9
c. x^2 + 3x + 9
d. 3x + 9

Answer 1

f is currently composed of x, we want to compose it if g(x), so let x=g(x)

f(g(x)) = [g(x)]^2+3[g(x)]

but we know g(x) is just a name for: x-3 soo

f(g(x)) = (x-3)^2+3(x-3)

and simplify as needed

Answer 2

Aah, thank you! @amistre64

So the correct answer is just x^2 - 3x?

Answer 3

hmm lets test it out

(x-3)(x-3+3)

(x-3)(x) i like it

Answer 4

Thank you! <3