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Sudheesh Singanamalla Grade: 12

evaluate cosx . cos2x . cos3x !!


the answer is given as

cosx.cos2x.cos3x = 2*cosx*xos2x*cos3x/2 and so on until we get


[2 cos^2 3x + 2 cos 3x.cos x]/4 which is furthur equal to

[1+cos6x + cos4x + cos2x] / 4

please explain how this step has come from the previous step !

thanks in advance

7 years ago

Answers : (3)

Amit Saxena
35 Points

Dear Sudeesh,

[2 cos^2 3x + 2 cos 3x.cos x]/4 : 

you can use Cos (A+B) + Cos(A-B) for the last two terms and Cos 2A = 2Cos2A - 1 for the first term, in result you will get as  :  

[1+cos6x + cos4x + cos2x] / 4


All the best.                                                           

AKhilesh Shukla



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7 years ago
Mayank Jain
37 Points

Dear Sudheesh

See The Pic for the solution.


7 years ago
Sudheesh Singanamalla
114 Points

Thank you everyone

6 years ago
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