Question

Given that vector |P + Q| = vector|P – Q|. This can be true when : 

(a) vector P = vector 0

(b) Q = 0

(c) Neither P nor Q is a null vector.

(d) vector P is perpendicular to vector Q.

Answer 1

Answer is (b) Q = 0

If P + Q = P - Q. Then Q = -Q.

which is possible when Q = 0 (null vector).