If $\displaystyle f$ is continuously differentiable in $\displaystyle \mathbb R^2$, $\displaystyle g$ is continuously differentiable in $\displaystyle \mathbb R$, $\displaystyle a$ a constant real, how to calculate the derivative of $\displaystyle \int_a^{g(x)}f(x,t)dt$ with regard to $\displaystyle x$ (not by numerical methods)? Thanks.