已知x/y=2/7,则x²-3xy+2y²/2x ²-3xy+7y²的值是()
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已知x/y=2/7,则x²-3xy+2y²/2x ²-3xy+7y²的值是()
A.28/103 B.4/103 C.20/103 D.7/103
A.28/103 B.4/103 C.20/103 D.7/103
(x^2-3xy+2y^2)/(2x^2-3xy+7y^2)
=[(x/y)^2-3(x/y)+2]/[2(x/y)^2-3(x/y)+7]
=[(2/7)^2-3×(2/7)+2]/[2×(2/7)^2-3×(2/7)+7]
=(2^2-3×2×7+2×7^2)/(2×2^2-3×2×7+7×7^2)
=(4-42+98)/(8-42+343)
=60/309
=20/103
=[(x/y)^2-3(x/y)+2]/[2(x/y)^2-3(x/y)+7]
=[(2/7)^2-3×(2/7)+2]/[2×(2/7)^2-3×(2/7)+7]
=(2^2-3×2×7+2×7^2)/(2×2^2-3×2×7+7×7^2)
=(4-42+98)/(8-42+343)
=60/309
=20/103
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