[问答题]
Three point charges are arranged at the cornyzle ektvj m8:ke./*te4y0 h;ers of abupbt2gf*9j, pp, vw.fg 6u f3 square of side L as shown in Fig. 17–25. What is the potential at the fourth corv6u2tg9,p* jpf gfbf w.3 ub,pner (point A), taking $V\,=\,0$ at a great distance?
