已知X/Y=2/7, 求X2-3XY+2Y2/2X2-3XY+7Y2的值
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已知X/Y=2/7,求X2-3XY+2Y2/2X2-3XY+7Y2的值已知X/Y=2/7,求X2-3XY+2Y2/2X2-3XY+7Y2的值已知X/Y=2/7,求X2-3XY+2Y2/2X2-3XY+
已知X/Y=2/7, 求X2-3XY+2Y2/2X2-3XY+7Y2的值
已知X/Y=2/7, 求X2-3XY+2Y2/2X2-3XY+7Y2的值
已知X/Y=2/7, 求X2-3XY+2Y2/2X2-3XY+7Y2的值
X/Y=2/7,则X=2Y/7,
设Y=7t,则X=2t
X²-3XY+2Y²/2X²-3XY+7Y²
=(4t²-42t²+98t²)/(8t²-42t²+343t²)
=60t²/309t²
=20/103
(x^2-2xy+2y^2)/(2x^2-3xy+7y^2) [分子,分母同时除以y^2]
=[(x/y)^2-3(x/y)+2]/[2(x/y)^2-3(x/y)+7] [把x/y=2/7代入]
=[(2/7)^2-3(2/7)+2]/[2(2/3)^2-3(2/7)+7] [分子,分母同时乘以7^2]
=(2^2-3*2*7+2*7^2)/(2*2^2-3*2*7+7*7^2)
=60/309=20/103
X/Y=2/7，则X=2Y/7，
设Y=7t，则X=2t
X²-3XY+2Y²/2X²-3XY+7Y²
=(4t²-42t²+98t²)/(8t²-42t²+343t²)
=60t²/309t²
=20/103
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