I have the formula for this problem (the green) but I can't find the inverse easily. Is there a trick that's appropriate for a AP Calc class? Thanks!
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$f(x) = 2x^3-3x$ notice that $f(1) = -1 \implies f^{-1}(-1) = 1$ using your formula, $(f^{-1})'(-1) = \dfrac{1}{f'[f^{-1}(-1)]} = \dfrac{1}{f'(1)}$ can you finish it up?