For three non-coplanar vector p,q and r, it is given that [pqr]a=q×r [pqr]b=r×p and [pqr]c=p×q ∴a,b,c are reciprocal system vectors of vectors p,q,c,so [abc]p=b×c...(i) [abc]q=c×a...(ii) and [abc]r=a×b...(iii) ∵a,b and c are coterminous edges of a parallelopiped, so height with the base have a and c is ‌