当3m=2n时,分式m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)=?

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当3m=2n时,分式m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)=?

当3m=2n时,分式m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)=?
当3m=2n时,分式m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)=?

当3m=2n时,分式m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)=?
m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)
=[m(m-n)+n(m+n)-n^2]/(m^2-n^2)
=m^2/(m^2-n^2)
=1/(1-(n/m)^2)
=1/(1-(3/2)^2)
=4/(4-9)
=-4/5

m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)
=m(m -n)/(m^2-n^2) +n(m +n)/(m^2-n^2)-n^2 /(m^2-n^2)
= (m^2 -mn)/(m^2-n^2) +(mn +n^2)/(m^2-n^2)-n^2 /(m^2-n^2)
= (m^2 -mn +mn +n^2 -n^2)/(m^2-n^2)
= m^2/...

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m/(m+n)+n/(m-n)-n^2 /(m^2-n^2)
=m(m -n)/(m^2-n^2) +n(m +n)/(m^2-n^2)-n^2 /(m^2-n^2)
= (m^2 -mn)/(m^2-n^2) +(mn +n^2)/(m^2-n^2)-n^2 /(m^2-n^2)
= (m^2 -mn +mn +n^2 -n^2)/(m^2-n^2)
= m^2/(m^2-n^2)
=1/(1 -n^2/m^2)
又3m=2n
故:n/m = 3/2
即:n^2/m^2 = 9/4
即:1/(1 -n^2/m^2) =1/(1 - 9/4)=-4/5

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