1. Three points P, Q and R have position vectors p, q and r respectively, where: p=8i+11j, q=7i-5j and r=2i+4j. Write down the vectors QP and QR and show that they are not perpendicular. Hence determine the angle PQR. 2. |QP|.|QR|cos(theta) 3. QP= QO+OP=i+16j QR=QO+OR=-5i+9j |QP|=root257 |QR|=root106 If the vectors are not perpendicular then a.b=0 a.b= QP=i+16j x QR=-5i+9j = (1)(-5)+(16)(9)=-5+144=139 - not perpendicular a.b=|QP|.|QR|cos(theta) cos(theta)=a.b/|QP|.|QR|=139/root257 x root106 = 32.6 Could anybody check to see how pathetic this attempt is, please?