Chapter 4.12, Problem 5P

If $u={\displaystyle {\int }_x^{y-x}\frac{\sin t}{t}}dt,$ find $\frac{\partial u}{\partial x},\frac{\partial u}{\partial y},$ and $\frac{\partial y}{\partial x}$ at $x=\pi /2,y=\pi$.

Hint: Use differentials.