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dimingc
Joined: 13 Mar 2005Posts: 8
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Posted: Fri Apr 01, 2005 9:20 pm Post subject: 請指教…F.2的幾何問題
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In the figure, ∠ABD=∠DBC=∠AED=30° and BD=DE.
Is ABC an equilateral triangle? Why?
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CMC
Joined: 23 Jan 2004Posts: 4
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Posted: Fri Apr 01, 2005 9:30 pm Post subject:
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Since ∠ABE=∠AEB, therefore triangle ABEis a isos. triangle.(opp.sides eq.∠s). ∠BAE=120° Since BD=DE, therefore ∠BAD=∠DAE=60° Since ∠BAC=∠ABC=60°, ∠ACB=60°
therefore triangle ABC is a equilateral triangle.
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dimingc
Joined: 13 Mar 2005Posts: 8
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Posted: Fri Apr 01, 2005 9:36 pm Post subject:
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But there is a problem.
That is BDE and ADC may not be a st. line.
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Illusion
Frequent VisitorJoined: 19 Jan 2005Posts: 37
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Posted: Fri Apr 01, 2005 11:04 pm Post subject:
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dimingc wrote:
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But there is a problem.
That is BDE and ADC may not be a st. line. |
呢條題目係係邊度搵出黎？ 如果係教科書， 有時佢俾幅圖，
幅圖顯示係直線，就即係話佢係直線－ －．．．
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dimingc
Joined: 13 Mar 2005Posts: 8
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Posted: Fri Apr 01, 2005 11:15 pm Post subject:
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Illusion wrote:
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dimingc wrote:
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But there is a problem.
That is BDE and ADC may not be a st. line. |
呢條題目係係邊度搵出黎？ 如果係教科書， 有時佢俾幅圖，
幅圖顯示係直線，就即係話佢係直線－ －．．．
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老師的Easter Holiday exercise
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