已知1/m-1/n=1,求5m+7mn-5n/2n-3mn-2m的值 计算 (2)a/b-b/a-a^2+b^2/ab

1/m-1/n=1
(n-m)/(mn)=1
n-m=mn
m-n=-mn
(5m+7mn-5n)/(2n-3mn-2m)
=[5(m-n)+7mn]/[2(n-m)-3mn]
=(-5mn+7mn)/(2mn-3mn)
=(2mn)/(-mn)
=-2
a/b -b/a -(a²+b²)/ab
=(a²-b²)/ab -(a²+b²)/ab
=(a²-b²-a²-b²)/(ab)
=-2b²/(ab)
=-2b/a
(7/6)x²y-(2/3)xy²+3/4z 题目有问题.
1-(x+2)/(1+x)
=[(1+x)-(x+2)]/(1+x)
=-1/(1+x)
[b/(a²-ab)+a/(b²-ab)]÷[(a-b)/ab]
=[b/a(a-b)+a/b(b-a)]÷[(a-b)/ab]
=[b/a(a-b)-a/b(a-b)]÷[(a-b)/ab]
=[(b²-a²)/[ab(a-b)]]×(ab)/(a-b)
=b²-a²

已知1/m-1/n=1,5m+7mn-5n/2n-3mn-2m=[5(1/m-1/n)+7]/[2(1/m-1/n)-3]=12/(-1)=-12
(2)a/b-b/a-(a^2+b^2)/ab
=(a²-b²-a²-b²)/ab
=-2b²/ab
=-2b/a
(3)7/6x^2y-2/3xy^2+3/4...