If f(x)=2x-4 and g(x)=2x^2-1 find g(f(x))(5)

Question

How do i solve this problem i don’t understand how to solve it please help me i need to do my homework question 

Answer 1

It might be clearer if the parentheses were correct.

find g(f(5))

so first calculate f(5), resulting in a number.

Then calculate g(that number)

Answer 2

g(f(x)) = 2(2x-4)² - 1

g(f(x)) = 2(4x² - 16x + 16) - 1

g(f(x)) = 8x² - 32x + 32 - 1

g(f(x)) = 8x² - 32x + 31

g(f(5)) = 8(5)² - 32(5) + 31

g(f(5)) = 200 + 160 + 31 = 391

Answer 3

First you need to find g(f(x)):

g(x)=2x²-1. Now, instead of x plug in f(x)=2x-4

g(f(x))=2(f(x))²-1=2(2x-4)²-1=|simplify it and then find value of the resulted expression for x=5|=

=2*2²(x-2)² -1=8(x-2)²-1.

g(f(5))=8*3²-1.=71