Question

Let f(x)=x^2 -81. Find f^1(x)

Answer 1

Hello,


I suppose you mean -1! else f(x)=f^1(x)

y=x²-81
-> x=y²-81 (exchahge x and y)
->y²=x+81 (solve for y)
$y= \sqrt{x+81} \ or \ y=- \sqrt{x+81}$ It is because (f^-1)(x) is not a function!

with x>=-81