Determine all pairs among the functions $1, x, \cos \pi x, \sin \pi x, e^x$, that are orthogonal with respect to the $\mathrm{L}^2$ inner product on $[-1,1]$.
3.2.30. Find two non-zero functions that are orthogonal with respect to the weighted inner product $\langle f, g\rangle=\int_0^1 f(x) g(x) x d x$.