If v→1+v→2 is perpendicular to v→1−v→2, then

If two vectors are normal to each other, then their dot product is zero.v→1+v→2⋅v→1−v→2=0⇒v12−v22=0⇒ v12−v22 ⇒ v1=v2  or  v→1=v→2