已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为

已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为
已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为

已知x/y=2/7,则x²-3xy+2y²/2x²-9xy+7y²的值为
你好!
(x²-3xy+2y²)/(2x²-9xy+7y²)
= [ (x/y)² - 3(x/y) + 2 ] / [ 2(x/y)² - 9(x/y) + 7] （分子分母同除以 y²）
= [ (2/7)² - 3×2/7 +2 ] / [ 2×(2/7)² - 9×2/7 + 7]
= (60/49) / (125/49)
= 12/25