Vectors-Please Help me out

if ur geometry is fine....
then vectors are just like bread and wine...... :P

use the property that...
the median from the vertex containing the right angle on the hypotenuse of a right-triangle
equals the bisected parts of the hypotenuse...!!

so lock option (A)

(\vec{a}-\vec{b}).(\vec{a}+\vec{b}) =0

|\vec{a}|^{2}-\vec{a}.\vec{b} +\vec{a}.\vec{b} -|\vec{b}|^{2} =0

|\vec{a}| =|\vec{b}|