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C4 identities

Stuck on 6b helpp
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you need to use one of the three expansions of Cos2Θ
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Mitul106
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Original post by the bear
you need to use one of the three expansions of Cos2Θ


Am i on the right track?
Original post by Mitul106
Stuck on 6b helpp


Have a gander at one of these, and see which is more appropriate:

[br]cos2x=cos2x−sin2x=2cos2x−1=1−2sin2x[br] [br]cos2x = cos^2 x - sin^2 x = 2cos^2 x - 1 = 1 - 2sin^2 x[br]

As it wants x=cos(theta) x = cos(theta) , then the most appropriate would be the second substitution above for cos2x cos2x , so you end up with a cos3x cos^3 x which can be substituted for x3 x^3 .

Hope this helps :smile:
(edited 7 years ago)

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