Question

if|p+q|=|p-q| then find angle between p and q

Answer 1

angle between them is 90

Answer 2

let, the angle between two vectors is @
now,
| p+q| =| p- q|
or, {p^2+ q^2+ 2pq cos@}^(1÷2) ={p^2+q^2- 2pq cos@}^(1÷2)

or, cos @= -cos@
or, 2 cos @= 0
or, @= 90° , 270°, ......., (2n +1)×90°
{where, n= 0, +/- 1, +/-2,...}