Question

Find the values of x for which f(x) = g(x). (Enter your answers as a comma-separated list.) f(x) = x2, g(x) = x + 20

Answer 1

Given
function f(x) = x²
function g(x) = x + 20

Solution:
Substitute f(x) with x² and substitute g(x) with (x + 20)
f(x) = g(x)
x² = x + 20

Move all terms to the left side. After moving, the positive ones become negative.
x² = x + 20
x² - x - 20 = 0

I break -x into -5x + 4x
x² - x - 20 = 0
x² - 5x + 4x - 20 = 0

Factorize x² - 5x
x² - 5x + 4x - 20 = 0
x(x - 5) + 4x - 20 = 0

Now factorize 4x - 20
x(x - 5) + 4x - 20 = 0
x(x - 5) + 4(x - 5) = 0

Separate (x - 5) from all terms using distributive property, the remaining one is (x + 4)
x(x - 5) + 4(x - 5) = 0
(x - 5)(x + 4) = 0

The solution
x - 5 = 0
x = 5
or 
x + 4 = 0
x = -4

f(x) and g(x) will be both equal if the value of x is either 5 or -4

Answer 2

 f(x) = x2 + 2x + 1, g(x) = 11x − 19 x2 + 2x + 1 = 11x - 19 x2 - 9x + 20 = 0 (x-4)(x-5) = 0 x = 4, 5