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Hilda
Joined: 15 Apr 2004Posts: 12
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Posted: Thu Apr 15, 2004 10:55 pm Post subject: 求△ABC的周長和面積.
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在△ABC中，∠A、∠B、∠C所對邊分別為a、b、c，若a、b是關於x的一元二次方程x^2-(c+4)x+4c+8=0的兩根，且sinA=9c/25a，求△ABC的周長和面積.
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me
Frequent VisitorJoined: 12 Feb 2004Posts: 194
Location: Hong Kong
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Posted: Thu Apr 15, 2004 11:20 pm Post subject: Re: 求△ABC的周長和面積.
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Hilda wrote:
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| 在△ABC中，∠A、∠B、∠C所對邊分別為a、b、c，若a、b是關於x的一元二次方程x^2-(c+4)x+4c+8=0的兩根，且sinA=9c/25a，求△ABC的周長和面積. |
sum of roots:a+b=c+4 product of roots:ab=4c+8
and sinA=9c/25a, so we can easily solve the triangle ABC.
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Hilda
Joined: 15 Apr 2004Posts: 12
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Posted: Fri Apr 16, 2004 11:18 pm Post subject: Re: 求△ABC的周長和面積.
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me wrote:
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Hilda wrote:
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| 在△ABC中，∠A、∠B、∠C所對邊分別為a、b、c，若a、b是關於x的一元二次方程x^2-(c+4)x+4c+8=0的兩根，且sinA=9c/25a，求△ABC的周長和面積. |
sum of roots:a+b=c+4 product of roots:ab=4c+8
and sinA=9c/25a, so we can easily solve the triangle ABC.
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你可否再清楚一點解釋怎樣利用a+b=c+4, ab=4c+8, sinA=9c/25a來解三角形ABC?勞煩晒!!!
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me
Frequent VisitorJoined: 12 Feb 2004Posts: 194
Location: Hong Kong
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Posted: Sat Apr 17, 2004 6:07 pm Post subject: Re: 求△ABC的周長和面積.
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Hilda wrote:
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me wrote:
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Hilda wrote:
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| 在△ABC中，∠A、∠B、∠C所對邊分別為a、b、c，若a、b是關於x的一元二次方程x^2-(c+4)x+4c+8=0的兩根，且sinA=9c/25a，求△ABC的周長和面積. |
sum of roots:a+b=c+4 product of roots:ab=4c+8
and sinA=9c/25a, so we can easily solve the triangle ABC.
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你可否再清楚一點解釋怎樣利用a+b=c+4, ab=4c+8, sinA=9c/25a來解三角形ABC?勞煩晒!!!
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make use of this:
or you may use area to solve it.
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