We can solve for x
f(x) = x^2 - 81
f(x) + 81 = x^2
√(f(x) + 81) = x
Your inverse function is
f-1(x) = √(x+81)
We have shown the positive branch of the square root. The inverse relation is actually double-valued, as x may be either sign and still give the same result for f(x).
f(x) = x^2 - 81
f(x) + 81 = x^2
√(f(x) + 81) = x
Your inverse function is
f-1(x) = √(x+81)
We have shown the positive branch of the square root. The inverse relation is actually double-valued, as x may be either sign and still give the same result for f(x).