Question

If f(x)=2x^2+8,what is the positive value of x for which f(x)=136

Answer 1

136 = 2x^2 + 8
128 = 2x^2
64 = x^2
8 = x

Answer 2

I would say the answer is 8:

f(x) = 2x^2 + 8
f(x) = 136
f(x) = f(x)
2x^2 + 8 = 136
Subtract both sides by 8
2x^2=128
Divide both sides by 2
x^2 = 64
Square both sides
x = 8