General

Gr. 12 Vectors Problems Help

I have encountered two vectors problems that I need clearing up on certain points:

1. Given tetrahedron ABCD such that Ab _l_ CD and AC_l_ BD, use any point P to prove that AD _l_ BD

Has anyone encountered a similar problem who can give me a clue where to place P?

2. A parallelpiped has one edge formed by vector u = [1,3,-2]. Determine two vectors that would result in a volume of 20 units^3.

Although I understand the formula would be 20=(vector u) dot (vector 1) cross (vector 2), the obvious problem of getting 6 variables upon expansion comes. Is there an easier way about actually finding the possible vectors?