Question: Let P = (x, y, z) , Q = (u, v, w) and R = (r, s, t) be points on the plane ax + by + cz = d.
(a) What is the relation between PQ→ × PR→ and the normal vector to the plane, ai→ + bj→ + ck→?
(b) Express PQ→ × PR→ in terms of x, y, z, u, v, w, r, s, t.
(c) Use the equation for the plane to eliminate z, w, and t from the expression you obtained in part (b), and simplify. Does your answer agree with what you said in part (a)?