快,急,
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快,急,快,急, 快,急,x/(x+y)+y/(x-y)-y^2/(x^2-y^2)=[x(x-y)+y(x+y)-y^2]/(x^2-y^2)=x^2/(x^2-y^2)=1/(1-(y/
快,急,
快,急,
快,急,
x/(x+y)+y/(x-y)-y^2/(x^2-y^2)
=[x(x-y)+y(x+y)-y^2]/(x^2-y^2)
=x^2/(x^2-y^2)
=1/(1-(y/x)^2)
x/5=y/3
y/x=3/5
原式=1/(1-3/5)=5/2
2.5