railajj1
幼苗
共回答了19个问题采纳率:100% 举报
1/(y^2+z^2-x^2)+1/(z^2+x^2-y^2) +1/(x^2+y^2-z^2)
=1/[y^2+z^2-(y+z)^2]+1/[z^2-y^2+(y+z)^2] +1/[(y+z)^2+y^2-z^2]
=1/(-2yz) + 1/(2z^2+2yz) +1/(2y^2+2yz)
=-1/2yz +1/2z(z+y) +1/2y(y+z)
=-x/2xyz-y/2xyz-z/2xyz
=-(x+y+z)/2xyz
=0
1年前
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