How do you find (fog)(x)(fog)(x) given f(x)=x^2+7f(x)=x2+7 and g(x)=x-3g(x)=x3?

1 Answer
Mar 26, 2017

(fog)(x)(fog)(x) can be written as f(g(x))f(g(x)). I prefer the latter notation, because it better illustrates that you substitute the equivalent of g(x)g(x) for every x that you see in f(x)f(x).

Explanation:

Given: f(x)=x^2+7f(x)=x2+7 and g(x)=x-3g(x)=x3

To find f(g(x))f(g(x)), we substitute x-3x3 for every x that we see in f(x)f(x):

f(g(x)) = (x-3)^2+7f(g(x))=(x3)2+7

Technically, we are done but it is better to simplify the right side:

f(g(x)) = x^2-6x+9+7f(g(x))=x26x+9+7

f(g(x)) = x^2-6x+16 larrf(g(x))=x26x+16 the answer