Given: $ y(n)=x(n)*h(n)=\int_{k=-\infty}^{\infty}x(\tau)h(t-\tau)d\tau $

- $ x(n)*h(n)=\int_{k=-\infty}^{\infty}x(\tau)h(t-\tau)d\tau $
- $ \tau'=t-\tau $
- $ x(n)*h(n)=\int_{k=\infty}^{-\infty}x(t-\tau')h(\tau')(-1)d\tau' $ from 1 and 2
- $ x(n)*h(n)=\int_{k=-\infty}^{\infty}h(\tau')x(t-\tau')d\tau' $
- $ x(n)*h(n)=h(n)*x(n) $