1. ## Trigonometric product

$Finding value of (0.5+\cos \alpha)\times(0.5+\cos 3\alpha)\times(0.5+\cos 9\alpha)\times(0.5+\cos 27\alpha)$

$Where \alpha =9^\circ}$

I have tried like this way

$let (x+\cos \alpha)(x+\cos 3\alpha)(x+\cos 9\alpha)(x+\cos 27\alpha)$

$which equals x^4+(\sum \cos \alpha)x^3+(\cos \alpha \cdot \cos 3\alpha)x^2+(\cos \alpha \cdot \cos 3\alpha\cdot \cos 9\alpha)x^2+\cos \alpha \cos 2\alpha \cos 3\alpha \cos 9\alpha \cos 27 \alpha$

How to go further. Help required. Thanks

2. ## Re: Trigonometric product

I had to write this on texmaker because I didn't know the code format on bos is different

Here is my solution.

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