Express product as a sum/different containing only sines or cosines.

sin4Asin2A=????

I stuck at beginning.

THX WHO HELP~!

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- Sep 11th 2008, 04:52 AMsanikuitrigo sum/different~do not do~!
Express product as a sum/different containing only sines or cosines.

sin4Asin2A=????

I stuck at beginning.

THX WHO HELP~! - Sep 11th 2008, 05:07 AMthelostchild
remember that

$\displaystyle \sin 2A=2\sin A \cos A$

(so obviously $\displaystyle \sin 4A = 2\sin2A \cos 2A$)

and $\displaystyle \cos 2A = \cos^2A - \sin^2 A$

make substitutions and simplify :) - Sep 11th 2008, 05:08 AMmr fantastic
See my reply in this thread for the formulae you need: http://www.mathhelpforum.com/math-he...dentities.html

- Sep 11th 2008, 05:20 AMMr.Greenanswer
sin4Asin2A=sin2(2A)sin2A

=2sin2Acos2Asin2A

=2(2sinAcosA)(1-2sin^2A)(2sinAcosA)

=8sin^2Acos^2A(1-2sin^2A)

=8sin^2A(1-sin^2A)(1-2sin^2A) - Sep 11th 2008, 05:34 AMmr fantastic
- Sep 11th 2008, 06:43 AMsanikui
I got it from Mr.fantastic.

THx Mr.Green ans Mr.fantastic~!!

I'm continues do my homework~!!(Happy)