Question 83404
given f(x) = x^2 + 9

Let y = x^2 + 9

To find f^-1 we first interchange x and y

==>  x = y^2 + 9

==>  x - 9 = y^2

==> sqrt(x - 9) = y

Thus f^-1 (x) = sqrt(x - 9)