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x+y=s xy=tx^2+y^2=(x+y)^2-2xy=s^2-2tx*2+y*2+x+y=18 x*2+xy+y*2=19s^2-2t+s=18(1)s^2-2t+t=9(2)由(1)得:t=(s^2+s-18)/2代入(2)得到:s^2-(s^2+s-18)/2=9s(s-1)=0s=0 t=-9或s=1 t=-8s=0 t=-9,也就是x+y=0…
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