Prove that the elastic potential energy density of a stretched wire is half the product of stress and strain.

Prove that for any quadrilateral with diagonals perpendicular, the area.ls half the product of the diagonals:

Potential energy of a system of charges is directly proportional to the product of charges and inversely to the distance between them.Prove the above statement.

Potential energy of a system of charges is directly proportional to the product of charges and inversely to the distance between them.Two point charges 3 x 10^(-8) C and - 2 x 10^(-8) C are separated by a distance of 15cm. At what point on the line joining the charges the potential is zero?