用所学的只是解决下列问题:1.已知x分之1-y分之1=5,求8y-9xy-8x分x+7xy-6y

问题描述:

用所学的只是解决下列问题:1.已知x分之1-y分之1=5,求8y-9xy-8x分x+7xy-6y

1/x-1/y=5
两边乘xy
y-x=5xy
x-y=-5xy
所以原式=[6(x-y)+7xy]/[-8(x-y)-9xy]
=[6(-5xy)+7xy]/[-8(-5xy)-9xy]
=-23xy/(31xy)
=-23/31