Derivative of e^x with respect to y I recently came across a question that asked for the derivative of $e^x$ with respect to $y$. I answered $\frac{d}{dy}e^x$ but the answer was $e^x\frac{dx}{dy}$. How is that the answer? I am confused.
If $x$ is a function of $y$ then the given answer follows by the chain rule:

$$\frac {\text d}{\text dy} \left(e^x\right) = e^x \cdot \frac {\text d}{\text dy}(x)$$
I feel the question needs to be clearer. It needs to be mentioned what exactly is $y$. Like one of the comment says, $y$ may not be a dependent variable. In that case, $\frac{\partial{e^{x}}}{\partial{y}}$ equates to zero. However, in case $x$ is a function of $y$ then, $\frac{de^{x}}{dy}$ can be written as $$\frac{de^{x}}{dy}×\frac{dx}{dx}$$ $$=\frac{de^{x}}{dx}×\frac{dx}{dy}$$ This gives the answer as, $$e^{x}×\frac{dx}{dy}$$