Three identical positive charges, +q, are placed at three of the four corners of a square with side lengths d. Derive the expressions and fill the blanks. (a) What is the electric potential at the corner that is missing a charge?

(b) What is the work required to move a fourth charge, +q, from an infinite distance to the corner that is missing a charge?

(c) Check your answer to part (b) by calculating the difference between the electrical potential energy in the cases of three charges and four charges.