SOLUTION: Find the indicated composition. {{{f(x)=17x^2-6x}}} {{{g(x)=8x-5}}} (f*g)(8)

Algebra ->  Functions -> SOLUTION: Find the indicated composition. {{{f(x)=17x^2-6x}}} {{{g(x)=8x-5}}} (f*g)(8)      Log On


   

Question 230938: Find the indicated composition.
f%28x%29=17x%5E2-6x
g%28x%29=8x-5
(f*g)(8)
Answer by likaaka(51) About Me  (Show Source):
You can put this solution on YOUR website!
First evaluate (f*g)(x), then substitute in x=8
Given f%28x%29=17x%5E2-6x and g%28x%29=8x-5, then (f*g)(x)=%2817x%5E2-6x%29%288x-5%29
Perform FOIL
(f*g)(x)=%2817x%5E2%29%288x%29+%2B+%2817x%5E2%29%28-5%29+%2B+%28-6x%29%288x%29+%2B+%28-6x%29%28-5%29
(f*g)(x)=136x%5E3-85x%5E2-28x%5E2%2B30x
(f*g)(x)=135x%5E3-113x%5E2%2B30x
Now substitute in x=8
(f*g)(8)=135%288%5E3%29-113%288%5E2%29%2B30%288%29
(f*g)(8)=135(512)-113(64)+30(8)
(f*g)(8)=69120-7232+240
(f*g)(8)=62136