<p>This deals with inverse functions:</p>
<p>suppose g(x) is the inverse of f(X) and G(X) = 1/g(X). If f(3) = 3 and f'(3) = 1/9, find G'(3).</p>
<p>Does anyone know how to answer this question?</p>
<p>Thanks.</p>
<p>anyone? bump</p>
<p>There's a formula for g'(x) that I can never actually memorize.</p>
<p>But you can re-derive it with something along the lines of:</p>
<p>Let y = f(x). Then f-inverse(y) = x, or g(y) = x. So g'(y)*y' = 1 and y' = 1/[g'(y)] = 1/[g'(f(x))].</p>
<p>Now the derivative of G'(x) is a function of g(x) using the quotient rule...</p>
<p>And that should give you enough to keep moving...</p>