15) Joining the points P1 and P2 with the origin
O, and applying triangle law, from the triangle
OP1P2, we have
1
1 2
OP
uuur+P P
uuuur  =
OP 2
uuuur
Using the properties of vector addition, the
above equation becomes
1 2
P P
uuuur  =
2
1
OP
OP
−
uuuur
uuur
i e