Demonstrate , using the definition of the dot product, that the length of the vectors a and b are equal if an only if the diagonals of the quadrilateral OAQB are orthogonal.

A Q

O B

its meant to be a rhombus

Hint: Use that if (OA-OB) is perependicualr to (OA+OB) then OA = OB and vice versa.

P.S dont tell me the answer just need some help of what to do help much appreciated