可吾可以幫我下,,仲有幾條三角函數=2=

圖片參考：http://img6.imageshack.us/img6/1648/screenhunter06apr301729.gif


http://img6.imageshack.us/img6/1648/screenhunter06apr301729.gif

2010-04-30 18:55:36 補充：
你打錯左條問題。

第9題:http://j.imagehost.org/0703/ScreenHunter_15_Apr_30_18_53.gif

這裏可以幫到你
http://actioni.w7.c361.net/yahoo.com.hk/hk/auction/178987536

1 cot(A+B)=cotAcotB-1/cotA+cotB
L.H.S. = cot(A+B)
= 1/ tan (A+B)
= [1 - tan A tan B]/[tanA + tanB]
= [ 1 - 1/cotAcotB] / [1/cotA + 1/cotB]
= [(cotAcotB - 1)/(cotAcotB)]/[(cotB+cotA)/(cotAcotB)]
= (cotAcotB -1)/(cotB-cotA)
= R.H.S.

2010-04-30 17:57:49 補充：
2 cosA+sinA/cosA-sinA = tan(π/4+A)
R.H.S. = tan(π/4+A)
= (tanπ/4+tanA)/(1-tanπ/4 tanA)
= (1+tanA)/(1-tanA)
= (1 + sinA/cosA)/(1 - sinA/cosA)
= [(cosA + sinA)/cosA]/[(cosA-sinA)/cosA]
= (cosA+sinA)/(cosA-sinA)]
= L.H.S.

2010-04-30 17:57:57 補充：
3在三角形ABC中 cosA=sinBsinC-cosBcosC
A = 180deg - B - C
L.H.S. = cosA
= cos(180deg - B - C)
= cos(B+C)
= sinBsinC - cosBcosC
= R.H.S.

2010-04-30 17:58:04 補充：
4 sin5x/sinx - cos5x/cosx = 4 - 8sin ^ 2 x
L.H.S. = sin5x/sinx - cos5x/cosx
= (sin5xcosx - cos5xsinx)/(sinxcosx)
= sin(5x-x)/sinxcosx
= sin4x/sinxcosx
= 2sin2xcos2x / (sin2x /2)
= 4sin2xcos2x / sin2x
= 4cos2x

2010-04-30 17:58:17 補充：
R.H.S. = 4-8sin^2 x
= 4(1-2sin^2 x)
= 4cos2x
= L.H.S.

2010-04-30 17:58:26 補充：
5 cos3x/sinx + sin3x/cosx =2cot2x
L.H.S. = cos3x/sinx + sin3x/cosx
= (cos3xcosx + sin3xsinx)/sinxcosx
= cos(3x-x)/(2sinxcosx/2)
= 2cos2x/sin2x
= 2cot2x
= R.H.S.

2010-04-30 17:58:32 補充：
6 2tanx/1+ tan ^ 2 x =sin2x
L.H.S. = 2tanx /(1+tan^2 x)
= 2tanx / sec^2 x
= 2(sinx/cosx)/(1/cos^2 x)
= 2sinxcosx
= sin2x
= R.H.S.

2010-04-30 17:58:38 補充：
7 三角形abc中 角c=90度 求證:sin(A-B) = cos2B
A = 90deg - B
L.H.S. = sin(A-B)
= sin(90deg - B - B)
= sin(90deg - 2B)
= cos2B
= R.H.S.

2010-04-30 17:58:55 補充：
其餘2題~1眼睇唔出~唔識~

2010-04-30 18:00:23 補充：
佩服~~這麼快就做完了~