主項變換!!

(x + a)/(x - b) = c/d
d(x + a) = c(x - b) 消除除號
dx + da = cx - cb 刪括號
ad + bc = cx - dx 把同類項合併
ad + bc = x(c - d) 因式分解
(ad + bc)/(c - d) = x 將c - d調到另一方
x = (ad + bc)/(c - d) 把上式寫成x =

(x+a)/(x-b)=c/d

x+a=(x-b)c/d

x+a=cx/d-bc/d

x-cx/d=-bc/d-a

x(1-c/d) = -bc/d-a

x = (-bc/d-a)/(1-c/d)

x=(bc/d+a)/(c/d-1)

x=(bc+ad)/(c-d)

2007-01-04 19:42:43 補充：
最後果度係上下乘個d上去可以寫詳細D