f(x) = x² + 4
y = x² + 4
First, I reverse the equation to be
x² + 4 = y
Second, we need only x to remain on the left side and we need to move the others to the right side
x² + 4 = y
x² = y - 4
x = √(y - 4)
Last, change into invers function
f⁻¹(x) = √(x - 4)
