x/(x^2+1)=2/5
1/(x+1/x)=2/5
x+1/x=5/2
x^2/(x^4+1)=1/(x^2+1/x^2)=1/[(x+1/x)^2-2]=1/[(5/2)^2-2]=1/(25/4-2)=1/(17/4)=4/17
第二题目中有y吗?
x/(x^2+1)=2/5
1/(x+1/x)=2/5
x+1/x=5/2
x^2/(x^4+1)=1/(x^2+1/x^2)=1/[(x+1/x)^2-2]=1/[(5/2)^2-2]=1/(25/4-2)=1/(17/4)=4/17
第二题目中有y吗?