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Trignometry

Blazing goIITian

Joined:	18 Feb 2007
Post:	1042

11 Mar 2007 17:52:04 IST

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938

Plz Solve: Trigo

None

prove that

sin3x+sin2x-sinx=4sinxcosx/2cos3x/2

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Comments (4)

amaron

Hot goIITian

Joined: 26 Jan 2007

Posts: 156

11 Mar 2007 17:58:43 IST

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sin3x+sin2x-sinx=4sinxcosx/2cos3x/2

sin3x+sin2x-sinx=sinx(2(cosx +cos2x)) as 2cosx/2cos3x/2 =cosx +cos2x

sin3x+sin2x-sinx=2sinxcosx + 2sinxcos2x
implies,
sin3x-sinx =2sinxcos2x which is obvious.

That solves the problem!

shine

Scorching goIITian

Joined: 2 Mar 2007

Posts: 273

11 Mar 2007 18:04:25 IST

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(sin3x-sinx) + sin2x
=(2cos2xsinx) + 2sinxcosx
=2sinx(cos2x+cosx)
=2sinx.2cos3x/2 cosx/2
proved!!
cheers>!!!!!!!!

Gaurav |spideyunlimited| Ragtah

Moderator

Joined: 16 Dec 2006

Posts: 3373

4 Aug 2007 17:44:29 IST

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Priyesh heres the solution

sin3x + sin2x - sinx
= sin3x + 2cos3x/2 sinx/2
= sin(3/2x + 3/2x) + 2cos3x/2 sinx/2
= 2sin3x/2 cos3x/2 + 2cos3x/2 sinx/2
= 2cos3x/2 ( sin3x/2 + sinx/2)
= 2cos3x/2 (2sinx cosx/2)
= 4sinx cosx/2 cos3x/2

* PLZ RATE *

Madmax

Blazing goIITian

Joined: 24 Dec 2007

Posts: 1111

6 Sep 2008 19:49:48 IST

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Nice method spidey!!

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