7. Three positive charges are located at the corners of an equilateral triangle as in Figure P24.7. Find an expression for the electric potential at the center of the triangle. 8. In the rectangle of Fig. 24-55, the sides have lengths 5.0 cm and 15.0 cm, q,=-5.0uC and g = +2uC. With V=0 at infinity, what is the electric potential at (a) corner A and (b) corner B? (c) How much work is required to move a charge q3 =+3.0 uC from B to A along a diagonal of the rectangle? (D