Prove :

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- August 5th 2009, 07:29 AMdhiabProve : cosx,cos2x,cos4x,cos6x
- August 5th 2009, 07:58 AMGrandad
Hello dhiabBegin with , and use the formulae for the cosines of multiple angles in terms of powers of (for instance, here). This expression immediately reduces to and the result then follows.

Grandad - August 5th 2009, 09:30 AMred_dog
Another approach: