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Erica
Joined: 11 Aug 2004Posts: 9
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Posted: Fri Jan 21, 2005 7:48 pm Post subject: ╛Maths Q
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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?
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Wilson
Frequent VisitorJoined: 20 Oct 2004Posts: 74
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Posted: Fri Jan 21, 2005 11:18 pm Post subject: Re: ╛Maths Q
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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： |
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Andy
Frequent VisitorJoined: 28 Oct 2003Posts: 391
Location: Hong Kong
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Posted: Fri Jan 21, 2005 11:47 pm Post subject:
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As , we have . The values of a and sin A are deduced as what Wilson did._________________
Patience and tolerance are necessarily demanded Year-round.
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cs55555
Joined: 23 Aug 2004Posts: 19
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Posted: Sat Feb 05, 2005 8:46 pm Post subject:
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Andy wrote:
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| As , we have .
The values of a and sin A are deduced as what Wilson did.
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我唔明點解會咁
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142857
Joined: 01 Sep 2004Posts: 13
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Posted: Sat Feb 05, 2005 9:46 pm Post subject:
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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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