[填空题]
Repeat Problem 14 for thecn aun c(*pep17h(1 kmq /g1ir case whenyi8 ro9p zee-uq04,mb two of the positive charges, on opposite corne eb,ro 4mpey-zq09u 8irs, are replaced by negative charges of the same magnitude (Fig. 16–51).
$F_4$ = $ \times10^{ 7}\,N$
$\theta$ = $^{\circ}$
