jika f(x)=x2-2x-8.Tentukan f^-1 (x) apabila fof^-1(x)=x

[tex]f o f^{1-} =x \\ (x^{2} -2x-8) o f^{-1} =x\\ ( f^{-1})^{2} -2 ( f^{-1} )-8=x \\ ( f^{-1})^{2} -2 ( f^{-1} )=x +8 \\ ( f^{-1})^{2} -2 ( f^{-1} )+4=x +8+4 \\ ( f^{-1}-2 ) ^{2} =x +12\\ ( f^{-1}-2 ) = \sqrt{ x +12}\\ f^{-1} = \sqrt{ x +12}+2\\ [/tex]