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Mathematics

Description

How to change cos4x into 2cos^2 2x-1?

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Explanation & Answer

cos4x

cos(2x + 2x)

cos2xcos2x - sin2xsin2x

cos^2 2x - sin^2 2x

As sin^2 2x = 1 - cox^2 2x, So

cos^2 2x - (1 - cos^2 2x)

cos^2 2x - 1 + cos^2 2x

cos^2 2x + cos^2 2x - 1

2cos^2 2x - 1

Hence

cos4x = 2cos^2 2x - 1


Anonymous
Very useful material for studying!

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