x/(x-1)-2/(x+1)=4/(x2-1)两边同乘（x+1)(x-1)时,右边（2X-1）怎么没的?

Question

x/(x-1)-2/(x+1)=4/( x2 -1)
两边同乘（x+1)(x-1)时,右边（2X-1）怎么没的?

Answer 1

x²-1=(x+1)(x-1),所以当两边同时乘以(x+1)(x-1),右边的分母就与(x+1)(x-1)相消了