已知1/x - 1/y =5,则2X+5XY-2Y/X-2XY-Y 的值是...
问题描述:
已知1/x - 1/y =5,则2X+5XY-2Y/X-2XY-Y 的值是...
答
1/x-1/y=5,两边同时乘XY,得y-x=5XY
2x+5xy-2y=2x+y-x-2y=x-y
x-2xy-y=(x-y)(1+2/5)
2X+5XY-2Y/X-2XY-Y=(x-y)/(x-y)(1+2/5)=5/7