消费者均衡的等边际法则（Equal Marginal Principle）表达式为（ ）。
$MU_1 / P_1 = MU_2 / P_2$
$MU_1 / MU_2 = P_2 / P_1$
$MU_1 imes P_1 = MU_2 imes P_2$
$MU_1 + P_1 = MU_2 + P_2$
