# Math Help - substitution problem

1. ## substitution problem

If f is continuous on [0, $\pi$], use the substitution $u = \pi - x$ to prove that:

$\int_0^{\pi}xf(sinx)dx = \frac{\pi}{2}\int_0^{\pi}f(sinx)dx$

Completely lost here. $du = -1dx$ and I don't know how to start from there.

2. From

\begin{aligned}
u&=\pi-x\\
du&=-dx
\end{aligned}

we may derive

\begin{aligned}
x&=\pi-u\\
dx&=-du.
\end{aligned}

Hope this helps!