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Erica

Joined: 11 Aug 2004Posts: 9

Posted: Fri Jan 21, 2005 7:48 pm    Post subject: ╛Maths Q

1. 在三角形ABC中,已知A=60度,b=1,三角形ABC面積=根號3, 求(a+b+c)/(sinA+sinB+sinC) 2. 在三角形ABC中,a=m(m屬於正實數), b=6, A=30度, 要使c分別有一解,

兩解,無解,相應的m應滿足甚麼條件?

Wilson

Frequent VisitorJoined: 20 Oct 2004Posts: 74

Posted: Fri Jan 21, 2005 11:18 pm    Post subject: Re: ╛Maths Q

1. 三角形面積
Cosine rule:
Sine rule: ,
(但我覺得會有更快的方法。)

2.

Discriminant =
c 有一解:
c 有兩解: or
c 為無解:

Andy

Frequent VisitorJoined: 28 Oct 2003Posts: 391

Location: Hong Kong

Posted: Fri Jan 21, 2005 11:47 pm    Post subject:

As , we have . The values of a and sin A are deduced as what Wilson did._________________

Patience and tolerance are necessarily demanded Year-round.

cs55555

Joined: 23 Aug 2004Posts: 19

Posted: Sat Feb 05, 2005 8:46 pm    Post subject:

Andy wrote:

As , we have .

The values of a and sin A are deduced as what Wilson did.

我唔明點解會咁

142857

Joined: 01 Sep 2004Posts: 13

Posted: Sat Feb 05, 2005 9:46 pm    Post subject:

Let a/sinA=b/sinB=c/sinC=k then a=ksinA, b=ksinB, c=ksinC (a+b+c)/(sinA+sinB+sinC) =k(sinA+sinB+sinC)/(sinA+sinB+sinC) =k

=a/sinA

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