 r square minus of 2 a r cos theta. Yes, 2 a by r theta raise to power minus half. HCl molecule could be 1 by r plus becomes equal to 1 by r cos theta. 1 by r plus how it comes theta. So, square of that will come, cube of that will come and minus a by r cos theta. So, you can do this plus will be here minus over potential energy. Now, the effect of external interface in this way are conservative forces and we can define the potential energy theta 2 that is it fine. So, minus of theta 1 the energy. Now, if we assume U 9 theta 2 this is minus of the internal product then when you subtract this is the energy.