Quick Trigonometry Identity Question Watch

Wish
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#1
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#1
Incorrect QuestionCan someone show me how \sin ^22\theta equals \cos4\theta?

EDIT: I meant how is \sin ^22\theta equal to 1-\cos 4\theta?
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Dadeyemi
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#2
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#2
its not
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rnd
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#3
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(Original post by Wish)
Can someone show me how \sin ^22\theta equals \cos4\theta?
Don't try to prove this. It isn't true.
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Wish
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#4
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Sorry, my bad.

I meant how is \sin ^22\theta equal to 1-\cos 4\theta?
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The Bachelor
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#5
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Use one of the cos double angle formulas.
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Dadeyemi
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#6
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I think you mean sin(2x)^2 = (1-cos(4x))/2

sin(x)^2 = (1-cos(2x))/2 is an identity you can use
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IChem
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#7
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(Original post by Wish)
Sorry, my bad.

I meant how is \sin ^22\theta equal to 1-\cos 4\theta?
\cos^2 \theta - \sin^2 \theta = \cos 2 \theta

Now set \theta = 2\theta and do a little bit of rearranging.
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The Bachelor
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#8
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(Original post by IChem)
\cos^2 \theta - \sin^2 \theta = \cos 2 \theta

Now set \theta = 2\theta and do a little bit of rearranging.
Not exactly the clearest way to put it, he means \cos^2 \alpha - \sin^2 \alpha = \cos 2 \alpha , and set \alpha = 2 \theta.


and dade is right, the right hand side of your equation needs to be divided by 2.
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