We know that
` | vec A + vec B| = sqrt( A^2 + B^2 + 2 AB cos theta)`
and ` | vec A - vec B| = sqrt (A^2 + B^2 -2 AB cos theta`
Squaring both the sides, we get
` 4 AB cos thete =0 ro cos theta =0 ro theta =90^@`
It means , the vectors ` vec A and vec B` are perpendicular to each other.
