设a+b+c+d=P则有：(x-a-b-c)/d+(x-b-c-d)/a+(x-a-c-d)/b+(x-a-b-d)/c=[(x-P)+d]/d+[(x-P)+a]/a+[(x-P)+b]/b+[(x-P)+c]/c=(x-P)(1/a+1/b+1/c+1/d)+4=4则有：x=P=a+b+c+d 祝学习进步
右边耐心通分就OK了
