Vectors

Hi i need to prove the following;

3 distinct points, P,Q are R have position vectors p,q and r respectfully. Show that P,Q and R are collinear (that is, all lie on a straight line) if   p x q + q x r + r x p = 0

op here, yer i noticed the dot product and figured out u meant cross product.

All 3 terms must add up to 0 and as all are non negative, as lengths are positive and sin(x) cannot be negative between 0-180 degrees then all the angles must be 0 or Pi, so they must lie on a straight line.