9 The point P lies on the side BC of AABC such that BP = t and CP = w. A If AB = u and AC =v, prove that u Xv=uXt+wXv. 10 Non-zero non-parallel vectors a, b and c are such that b × c = c X a. B t Prove that a + b = kc for some scalar k. 11 Prove that if the numbers p, q, r and s satisfy ps = qr, then (pa + qb) × (ra + sb) = 0.