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

Dear Sudeesh,

All the best.                                                           

AKhilesh Shukla

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Approved

Dear Sudheesh

See The Pic for the solution.

Approved

Thank you everyone