中四升中五數學

方法一 : 令 x = 2k , 3 = 3k
x / (x + y) = 2k / (2k + 3k) = 2 / (2 + 3) = 2/5
(x - y) / (x + y) = (2k - 3k) / (2k + 3k) = (2 - 3) / (2 + 3) = - 1/5
(x² - y²) / (x² + y²) = (4k² - 9k²) / (4k² + 9k²) = (4 - 9) / (4 + 9) = - 5/13
方法二 : x / (x + y) = = (x/y) / (x/y + y/y) = (2/3) / (2/3 + 1) = 2/5
(x - y) / (x + y) = (x/y - y/y) / (x/y + y/y) = (2/3 - 1) / (2/3 + 1) = - 1/5
(x² - y²) / (x² + y²) = (x²/y² - y²/y²) / (x²/y² + y²/y²) = (4/9 - 1) / (4/9 + 1) = - 5/13

2011-07-27 17:48:11 補充：
令 x = 2k , y = 3k