Factorize
.
By using the cross method, students may give the following two ‘possible answers’.
A.
B.
The correct answer is B. Some students may opt for A because the expression in A could give (so-called) the middle term . However, the constant term in A is (not , the correct one), hence A is not the answer.
Setting this type of question may remind students of the importance of checking the constant term.
Other examples like
=
A.
B.
=
A.
B.
Correct answers to the above are B. But some students may get it wrongly.
To set up such kind of questions, just consider two expressions:
All we need is setting
and
Yield
– – – – – – (*)
Then, we may put different positive integral value of and evaluate and finally .
Just give an example.
Put (say), by (*),
Just take and , thus
and hence
Hence we have two expressions
having the same ‘middle terms’ with constant terms differing in sign.
Of course, this article is rubblish once we have set program in calculators.
宜家覺得最恐怖係
聽見小學都用計數機教乘數
唔使諗乘數表
迴響 由 溟天凱 — 2008/11/16 @ 6:29 下午 |
唔係 fai….
想當年….. 媽媽指出九因歌是中國的國粹之一
之後在籐條輔助下,乘數表我當年背背下就識了 =_="
幾年前已有報導指外國的小朋友乘數根底薄弱…
仲唔到毒瘤像金融海嘯般殺到香港… = =
假若未來的主人翁 foundation 禁差….
佢地幾時先可以成為 “真正" 的主人翁?不解。
迴響 由 Ricky — 2008/11/17 @ 3:18 上午 |
我幫就讀小學五年級的侄兒看數學功課時,知道他是用心算的。
「理解」是重要,但相信「背誦」也有一定的正面作用。背誦國寶級文物「九因歌」,除了有助學習乘數,相信在小朋友的腦袋中,或多或少會產生某些網絡連繫(嗯,吹水的,手上沒有科學實證),腦部得以成長,對學習新事物或有所裨益(我用「或」,因為那是憑空猜測的。)
用一月、二月、三月等等,在某程度上比 January,February,March 更易於讓小朋友掌握。以英語來學乘法,可能較用中國人的「九因歌」困難。這個「國技」,絕對有保留的價值。
迴響 由 johnmayhk — 2008/11/17 @ 1:10 下午 |
“或多或少會產生某些網絡連繫.."
從認知心理學角度上 (記憶),這是有可能的。
至於是如何,小弟只知皮毛…
不敢在各高人前亂拋書包。
還望高手指點。
迴響 由 Ricky — 2008/11/17 @ 7:33 下午 |
真是有一間中學的數學老師,教學生用 program 計算 factorization 的題目,說用 cross method 浪費時間云云,留待中四時才學好了!
迴響 由 栗 — 2008/11/22 @ 6:17 下午 |
中二學 cross method?
迴響 由 W — 2009/03/25 @ 5:27 下午 |
Yes, nearly all methods and identities (including a^3 + b^3 , a^3 – b^3) about factorization are taught in F.2 in my school.
迴響 由 johnmayhk — 2009/03/25 @ 5:59 下午 |
唔知可唔可以在cross-method中用分數or小數點?
迴響 由 Lam Ho Hung — 2009/10/28 @ 5:29 下午 |
Cross method 的目的是因式分解。
比如要因式分解
你又厲害到,在沒有二次公式或/和計算機的幫助下,可以想到
從而得到
那麼 cross method 為何不能出現小數?
但如果同學用計算機的程式,進行以下的因式分解:
計算機顯示了
和
從而同學誤以為
的話,那當然是錯。
(注:正確是 )
又例如,你可以 cross method 分解
如果你厲害到,在沒有二次公式或/和計算機的幫助下,可以想到
從而得到
那麼 cross method 為何不能出現無理數?
注:題目應要說清楚容不容許 在答案中出現。
迴響 由 johnmayhk — 2009/10/28 @ 8:42 下午 |
我而+中二教identity and fatorization 都冇教cross method-.-我想學ah-.-
迴響 由 warren — 2009/11/01 @ 4:06 下午 |
我上年中二冇教cross method, 但中三有教, 所以我唸你中三都有得學嫁啦
迴響 由 winnie — 2011/09/23 @ 6:32 下午 |
我唔明hence 之後要點訐 比左個hence係唔係無關係 ? 只係叫你計埋佢?
迴響 由 zero — 2011/12/01 @ 10:39 下午 |
No . “Hence" means you have to use the result of the last question
迴響 由 Tony — 2012/03/31 @ 4:02 下午 |
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