Question

the resultant of two vectors P + q and P - Q when they are at right angles to each other is

Answer 1

r^2 = p^2 +q^2 (Since the angle is 90°)
r^2 = (p+q)^2 + (p-q)^2
      = p^2 + 2pq +q^2 + p^2 - 2pq +q^2
      = 2p^2 + 2q^2
   r   = √2(p^2 +q^2)