a4330811
幼苗
共回答了16个问题采纳率:87.5% 举报
1.因为abc=1,
所以a/(ab+a+1) + b/(bc+b+1) + c/(ac+c+1)
=a/(ab+a+1) + ab/(abc+ab+a) + c/(ac+c+abc)
=a/(ab+a+1) + ab/(1+ab+a) + c/[c(a+1+ab)]
=a/(ab+a+1) + ab/(ab+a+1) + 1/(a+1+ab)
=(ab+a+1)/(ab+a+1)
=1
2.因为xy=1,
则x=1/x
所以1/(1+x^2)+1/(1+y^2)
=1/(1+1/y^2)+1/(1+y^2)
=y^2/(1+y^2)+1/(1+y^2)
=(y^2+1)/(1+y^2)
=1
1年前
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