21.22.23题,

来源:学生作业帮助网 编辑:六六作业网 时间:2024/12/25 10:18:22
21.22.23题,21.22.23题, 21.22.23题,21、由(1/x)-(1/y)=3===>(y-x)/(xy)=3===>x-y=-3xy所以,原式=[2(x-y)-14xy]

21.22.23题,
21.22.23题,
 

21.22.23题,
21、
由(1/x)-(1/y)=3 ===> (y-x)/(xy)=3
===> x-y=-3xy
所以,原式=[2(x-y)-14xy]/[(x-y)-2xy]
=(-6xy-14xy)/(-3xy-2xy)
=(-20xy)/(-5xy)
=4
22、
x+2≠0,(x+3)/(x+4)≠0
所以,x≠-2,x≠-3,x≠-4
23、
===> (2x+1)(3x-1)<0
===> -1/2<x<1/3