Hi I'm learning about Electric Potential, and the Work Done for moving a charge in an electric field. The last equation really does not make sense to me. Please see the image attached.
I understand that to move a charge from point A to point B in an electric field (lets assume A is at a point which has a higher electric potential than point B) has a negative value for work done, and I understand the contents of the integral (simply the force required to move it multiplied by the length it moves). If the Electric Field was the other way around, the value for work done would be positive (it takes energy to move the charge from A to B now).
So why is the integral on the last line equal to zero? I'm probably missing something obvious here. Thanks