數學十分大的問題!!!各高手誠邀進入~請睗教!

2006-12-21 5:15 am

1)係唔係所有定理都有逆定理?(姐係用結果證原因)
例如
因為a,b係adj. angles on sti. line
so a+b=180度

逆定理就係:
因為a+b=180度
so AB係直線。

但係mid-pt.theorem 同intencept theorem老師話唔用得
我好唔服氣~明明o岩o既野點解唔用得?!
佢話只可以用係mc到\\ /
我證到mid-pt.theorem逆定理
雖然我證唔到intencept theorem逆定理,但我知係o岩~
真係好唔明囉!
請睗教!
另求intencept theorem逆定理的證明方法~多謝!!

2)仲有點解equal ratios theorem唔可以用係3條//的線到?
intencept theorem都可以砌到變成係三角形用la~
點解equal ratios theorem唔可以當個三角形上面分開左(姐係好似intencept theorem咁樣)

再次多謝大家抽空看我的問題!!
msn:
[email protected]

更新1:

3)點解0.999.....=1? 我知有得證~ 不過0.999.....只係十分接近1而唔係=1 我都知1/9+8/9=1 1/9=0.111... 8/9=0.888... =0.999... 但係都係唔明~請睗教!

回答 (5)

提摩太．艾力克

2006-12-23 2:20 am

3.設0.999...為x
x+1=1.999...
(x+1)-x=1.999...-(0.999...)
=1

所以0.999...=1

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johnnyxp2007

2006-12-22 6:38 am

3) 1/9=0.111...
8/9=0.888...
9/9=0.999...
9/9=1=0.999...

參考: myself

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貓朋

2006-12-21 10:21 am

1) Converse of Theorem is NOT necessary exits. Sorry. I forgot the exact form of intercept theorem and hence I cannot prove or disprove the converse here. On the other hand, it is not necessary to memorize the theorem since you can deduce what you need without the theorem.

2) 3 parallel lines are ok but the form of the theorem is not similar to the original one and the computation is much more complicate.

3) 0.99999...... is just another REPRESENTATION (表示方法) of the number 1. The actual theory behind is university level.

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Invalid username

2006-12-21 6:26 am

ANS Q.3 ONLY

GO TO http://hk.knowledge.yahoo.com/question/?qid=7006101602244 LA

2006-12-20 22:30:57 補充：
其實9/9可以等於1或0.99999999999999999.........為什麼?因為有一條定理證明0.999999999999999......=1Let x=0.99999999...............10x=9.9999999999........10x-x=9.99999.....-0.99999.......9x=9x=1所以0.9999999.........=1 ..........

參考: http://hk.knowledge.yahoo.com/question/?qid=7006101602244

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Chi Fung

2006-12-21 5:40 am

1) 逆定理問題:
這不一定是對,讓我舉個日常例子,
男人是人,但不是全世界的人是男人...
所以逆定理是有一定的限制...

2) intercept therom 吾係要直線咩@@?

3) 係米有寫幾位有效數字?

參考: Me

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