\[\boxed{\mathbf{71}\mathbf{.}}\]
\[\textbf{а)}\ y = \sqrt{x};\ \ x > 0;\ \ x = y^{2};\ \ \]
\[y > 0\]
\[x^{'}(y) = 2y;\]
\[f^{'}(x) = \frac{1}{(2y)^{'}} = \frac{1}{2\sqrt{x}}.\]
\[\textbf{б)}\ y = - \sqrt{x};\ \ x > 0;\ \ x = y^{2};\]
\[\ \ y < 0\]
\[x^{'}(y) = 2y;\]
\[f^{'}(x) = \frac{1}{(2y)^{'}} = - \frac{1}{2\sqrt{x}}.\]
\[\textbf{в)}\ y = \ln x;\ \ x > 0;\ \ x = e^{y};\ \]
\[\ y \in R\]
\[x^{'}(y) = e^{y};\]
\[f^{'}(x) = \frac{1}{e^{y}} = \frac{1}{x}.\]