Question

已知1/a+1/b=3 求(a-3ab+b)/(a+2ab+b)

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Answer 1

1/a+1/b=3
两边同乘以ab，得a+b=3ab
因此：(a-3ab+b)/(a+2ab+b)=0/(a+2ab+b)=0

Answer 2

原式=[(1/b)-3+(1/a)]/[(1/b)+2+(1/a)]又因为(1/a)+(1/b)=3,所以带进去后就等于0

Answer 3

因1/a+1/b=3，a+b=3ab,(a-3ab+b)/(a+2ab+b)=3ab-3ab/5ab
所以(a-3ab+b)/(a+2ab+b)=0

Answer 4

1/a+1/b=3
即：(a+b)/ab=3
即:a+b=3ab 将其带入
（a-3ab+b)/(a+2ab+b)=(a-a-b+b)/(a+2/3a+2/3b+b)=0/(5/3a+5/3b)=0

Answer 5

1/a+1/b=3 ，则(a+b)/ab=3
所以a+b=3ab
(a-3ab+b)/(a+2ab+b)
=(a+b-3ab)/(a+b+2ab)
=(3ab-3ab)/(3ab+2ab)
=0