S断氏世开：I=24/26.9=0.8922(mA)20000x0.0008922=17.8439(V)12-17.8439=-5.8439(V)S断开，A点电位为-5.8439VS闭歼者肢合：I=12/23.9=0.5021(mA)20000x0.0005021=10.042012-10.0420=1.9580(V)S闭合，嫌掘A点电位为1.9580V
