點解 (a+b)(c-d)
=ac+(-ad) + bc+(-bd)
(a+b)(c-d)
2007-01-07 8:24 pm
回答 (8)
2007-01-07 8:38 pm
✔ 最佳答案
首先, 你要明白四式運算中的兩條法則1) (a+b)c = ac + bc ;和
2) ab = ba
由此可見, 將(c-d)當成為上式(1)的c, 那麼(a+b)(c-d) = a(c-d) + b(c-d)
然後有了a(c-d)和b(c-d)
在case a(c-d)中,
將(c-d)當成為上式(2)的b, 那麼a(c-d) = (c-d)a
然後又將(c-d)當成為上式(1)的(a+b)﹑a當成為c, 那麼(c-d)a = ac - ad了;
在case b(c-d)都是同樣這麼做就會得出 b(c-d) = bc - bd了.
最後將兩個case結合起來, 就成了(a+b)(c-d) = ac - ad + bc - bd了.
再將它整理一下, 就是你的 = ac +(-ad) + bc +(-bd)吧。
參考: 我個腦
2007-01-09 7:13 am
(a+b)(c-d)
=(a+b)c+(a+b)(-d)
=ac+bc-ad-bd
=(a+b)c+(a+b)(-d)
=ac+bc-ad-bd
2007-01-09 6:31 am
(a+b)(c-d)
=(a+b)c+(a+b)(-d)
=ac+bc-ad-bd
=(a+b)c+(a+b)(-d)
=ac+bc-ad-bd
2007-01-07 11:24 pm
When you calculate it, you will find out that a*c=ac, a*(-d)=-ad, b*c=bc and b*(-d)=-bd.
Let me show you an example
(5+3)(4-2)
=20-10+12-6
=16
Let me show you an example
(5+3)(4-2)
=20-10+12-6
=16
參考: Me
2007-01-07 8:35 pm
(a+b)(c-d)
=(a+b) x (c-d)
咁你要分開乘...先睇a...
將a乘(c-d)先... =ac-ad
再睇b...將b乘(c-d)... =bc-bd
將兩個放埋一齊
=ac-ad+bc-bd
咁呢個同ac+(-ad)+bc+(-bd)係一樣
因為正負得負
=(a+b) x (c-d)
咁你要分開乘...先睇a...
將a乘(c-d)先... =ac-ad
再睇b...將b乘(c-d)... =bc-bd
將兩個放埋一齊
=ac-ad+bc-bd
咁呢個同ac+(-ad)+bc+(-bd)係一樣
因為正負得負
2007-01-07 8:32 pm
(a+b)(c-d)
=(a+b)(c)-(a+b)(d)
=ac+bc-ad-bd
=ac-ad+bc-bd
=ac+(-ad)+bc+(-bd)
=(a+b)(c)-(a+b)(d)
=ac+bc-ad-bd
=ac-ad+bc-bd
=ac+(-ad)+bc+(-bd)
2007-01-07 8:32 pm
當你展開（ａ＋ｂ）（ｃ－ｄ）
=ac+bc-ad-bd
=
=ac+bc-ad-bd
=
收錄日期: 2021-04-12 22:02:15
原文連結 [永久失效]:
https://hk.answers.yahoo.com/question/index?qid=20070107000051KK01560