 1 minus 2 a by r cos theta raise to power minus half. HCl molecule could be ok distance very final becomes 0 becomes 1 by r plus becomes 3.2 1 by r 2 comes 1 by r plus how it comes x raise to power n comes 1 into theta so square of that will come cube of that will come. So, any by r it becomes a by r understood all of I am cos theta you can do the same thing you can see here also rather minus plus will be here this will be plus and then will be minus over here. You are trying to find what is the potential energy or potential energy previous like this in this case ok. So, the let us say small this cos theta the force created by the stationary charges that is it fine and this is the work done. So, whatever this work done is we gain some kinetic energy also we have to make minus potential energy at theta 1 the energy. Now, if theta is equal to minus p assume u 90 to 2. So, this u minus of p dot this is the potential energy external energy ok. So, what is this do it external energy right. So, total will be minus of what internal potential energy when you subtract this will anyway.