### Home > A2C > Chapter 7 > Lesson 7.1.5 > Problem7-85

7-85.

Given $f\left(x\right) = 2x^{2} − 4$ and $g\left(x\right) = 5x + 3$, find the value of each expression below.

Substitute the quantity inside the parentheses ( ) for $x$ into the $f\left(x\right)$ or $g\left(x\right)$ equation and simplify.

1. $f\left(a\right)$

1. $f\left(3a\right)$

1. $f\left(a + b\right)$

$f\left(a + b\right) = 2a^{2} + 4ab + 2b^{2} − 4$

1. $f\left(x + 7\right)$

1. $f\left(5x + 3\right)$

1. $g\left(f\left(x\right)\right)$

$f\left(g\left(x\right)\right) = 10x^{2} − 17$