F.2因式分解X1

^2=２次方
cd^2-c^2d-c+d
=-c-c^2d+d+cd^2
=-c(1+cd)+d(1+cd)
=(d-c)(1+cd)

cd^2-c^2d-c+d
=cd(d-c)-(c-d) 用併項法,左邊抽cd右邊抽個負號
=cd(d-c)+(d-c) -(c-d) = +(d-c)
=(d-c)(cd+1) 抽個(d-c)出來唷**

2008-11-06 20:31:39 補充：
^ 呢個係代表次方
所以 cd^2 姐係cd``

cd``-c``d-c+d = cd²-c²d-c+d

=cd(d-c)+(-c+d)
=cd(d-c)+(d-c)
=(d-c)(cd+1)