31. 有一交流電路的v(t) = sin(314t + 60°)V,i(t) =cos(314t – 60°)A,此電路的實功率(有效功率)P 與虛功率(無效功率)Q 分別為:[自來水110](A)P =,Q = 500VAR(B)P =,Q = 250VAR(C)P = 500W,Q = 0VAR(D)P = 0W,Q = 500VAR