De moivre's theorem Watch

Davelittle
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#1
Report Thread starter 4 years ago
#1
Use De moire's theorem to find  \cos2\theta in terms of  \cos\theta

So I used DMT and took the real part but ended up with  \cos^2\theta + \sin^2\theta

How do I convert this to only  \cos\theta
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TeeEm
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#2
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(Original post by Davelittle)
Use De moire's theorem to find  \cos2\theta in terms of  \cos\theta

So I used DMT and took the real part but ended up with  \cos^2\theta + \sin^2\theta

How do I convert this to only  \cos\theta
a well known trigonometric identity from A level
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Davelittle
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(Original post by TeeEm)
a well known trigonometric identity from A level
Oops thought it was a + not a -, thanks haha
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TeeEm
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(Original post by Davelittle)
Oops thought it was a + not a -, thanks haha
should be a minus!
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Davelittle
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#5
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(Original post by TeeEm)
should be a minus!
Yup copied my working down wrong!
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TeeEm
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(Original post by Davelittle)
Yup copied my working down wrong!
all good
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