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1. Prove that 1+ cos2x + cos4x = cos2x (4cos^2x - 1)

I've tried this question so many times and I can't seem to do it! Help pls
2. (Original post by rn123)
Prove that 1+ cos2x + cos4x = cos2x (4cos^2x - 1)

I've tried this question so many times and I can't seem to do it! Help pls
By inspection you can see that if you leave the alone for now and only deal with you will be able to factor it out later on once you turn the 4x into 2x.

So apply the double formulae for cosine: and simplify from there.

Hint if you get stuck:
Spoiler:
Show
You will need to apply this twice.

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Updated: October 9, 2016
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