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...