hello, i know this is easy but i can't seem to solve it.

use vectors to prove:
that there exists a triangle with sides equal and parallel to the medians of any given triangle.

and

let u, v be two non-parallel, non zero vectors in a plane and let w be any other vector in the plane. prove that there exists unique scalars a, b such that w=au+bv

HELP IS SINCERELY VERY VERY APPRECIATED