For each of the given functions f(x) , find the derivative
\left(f^{-1}\right)'(c) at the given point c , first finding a=f^{-1}(c) .

a)f(x)= 3 x + 8 x^{9} ; c = -11

a =

\left(f^{-1}\right)'(c) =

b)f(x)= x^2 - 17 x + 83 on the interval [8.5,\infty) ; c = 17

a =

\left(f^{-1}\right)'(c) =

a)

b)

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