说明：  电压源的功率等于其电压乘以其供出的电流,电流源的功率等于其 电流乘以其端电压,而当前该条件均具备,直接计算即可。
(Voltage source of power equal to reveal the current voltage multiplied by the current source of power is equal to the current multiplied by its terminal voltage and current of the conditions are met, can be directly calculated.)