问题标题：
这几道数学题咋做啊1.已知x+y+z=0,则1/（y²+z²-x²)+1/(z²+x²-y²)+1/(x²+y²-z²)=2.若3x-4y-z=0,2x+y-8z=0,则（x+y-z)/(x-y+z)=3.已知a+b+c=0,且a,b,c均不为0,则a(1/b+1/c)+b(1/c+1/a)+c(1/a+1/
问题描述：
这几道数学题咋做啊
1.已知x+y+z=0,则1/（y²+z²-x²)+1/(z²+x²-y²)+1/(x²+y²-z²)=2.若3x-4y-z=0,2x+y-8z=0,则（x+y-z)/(x-y+z)=3.已知a+b+c=0,且a,b,c均不为0,则a(1/b+1/c)+b(1/c+1/a)+c(1/a+1/b)=
段起阳回答：
1.∵x+y+z=0∴y²+z²-x²=y²+z²-(y+z)²=-2yz同理z²+x²-y²=-2zxx²+y²-z²=-2xy原式=1/-2yz+1/-2zx+1/-2xy=(通分）-（x+y+z)/-2xyz...
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