- Prove that if u is orthogonal to both v and w, then u is orthogonal to both v + w.
- Prove that if u is orthogonal to both v and w, then u is orthogonal to sv + tw for all scalar s and t.

i think...

u * (vw) = 0 -> u*v + u*w = 0

u * (v + w) = 0 -> u*v + u*w = 0

.....