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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 !
6 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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```
6 years ago
Mayank Jain
37 Points
```										Dear Sudheesh
See The Pic for the solution.

```
6 years ago
Sudheesh Singanamalla
114 Points
```										Thank you everyone
```
6 years ago
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