I'm given a plane in R^3 that passes through the origin with normal vectora.I'm also given that P is spanned by u and v.

The question asked is to show that for everyxwithin P,x=proju(x) + projv(x).

All i can get from this is that the constants s and t for the parametric equation of the plane are equal to proju(x) and projv(x). other than this I really have no idea where to start.