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x^2+xy-4y^2=0,求x-y/x+y=?(2是平方)

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x^2+xy-4y^2=0,求x-y/x+y=?(2是平方)
y^2+16y^2=17y^2
x=(-y+-17^1/2y)/2
x=(-1+-17^1/2)/2y
1.x=(-1+17^1/2)/2y
(x-y)/(x+y)
=((-1+17^1/2)/2y-y)/((-1+17^1/2)/2y+y)
=(-3+17^1/2)/2/(1+17^1/2)/2
=(17^1/2-3)/(1+17^1/2)
=(17^1/2-3)(17^1/2-1)/16
=(17-4*17^1/2+3)/16
=(20-4*17^1/2)/16=(5-17^1/2)/4
2.x=(-1-17^1/2)/2y
(x-y)/(x+y)=((-1-17^1/2)/2y-y)/((-1-17^1/2)/2y+y)
=(-3-17^1/2)/2/(1-17^1/2)/2
=(-3-17^1/2)/(1-17^1/2)
=(3+17^1/2)(17^1/2-1)
=(3+17^1/2)(17^1/2+1)/16
=(20+4*17^1/2)/16
=(5+17^1/2)/4
(x-y)/(x+y)=(5+-17^1/2)/4