Math Forum :: View topic – 求△ABC的周長和面積.

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Hilda

Joined: 15 Apr 2004Posts: 12

Posted: Thu Apr 15, 2004 10:55 pm    Post subject: 求△ABC的周長和面積.

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.

me

Frequent VisitorJoined: 12 Feb 2004Posts: 194

Location: Hong Kong

Posted: Thu Apr 15, 2004 11:20 pm    Post subject: Re: 求△ABC的周長和面積.

Hilda wrote:

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.

Hilda

Joined: 15 Apr 2004Posts: 12

Posted: Fri Apr 16, 2004 11:18 pm    Post subject: Re: 求△ABC的周長和面積.

me wrote:

Hilda wrote:

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.

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!!!

me

Frequent VisitorJoined: 12 Feb 2004Posts: 194

Location: Hong Kong

Posted: Sat Apr 17, 2004 6:07 pm    Post subject: Re: 求△ABC的周長和面積.

Hilda wrote:

me wrote:

Hilda wrote:

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.

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!!!

make use of this:

or you may use area to solve it.

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