In an electric circuit, two resistors with resisitances x and y are connected in parrllel. In this case, if r is the combined resistance of these two resisitors ,then the reciprocal of r is equal to the sum of of the reciprocal of x and y. What is r in terms of x and y? 麻烦大家帮我翻译一下。。。谢谢了。。。