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# What rule is this?

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What rule is this? What is it called? Sin(2nX)/sin(nX) = 2Cos(nX)

Guest Aug 9, 2017
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#1
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What rule is this? What is it called? Sin(2nX)/sin(nX) = 2Cos(nX)

Hello guest!

sin 2x = 2 sin x cos x is one of the double angle functions

sin(2X)=2sin(X)*cos(X)

One can show this nicely over an addition theorem:

sin(x+y) = sin(x) * cos(y) + sin(y) * cos(x)

and this case has to do with double angles ...

sin(2x) = sin(x+x) = sin(x) * cos(x) + sin(x) * cos(x) = 2*sin(x)*cos(x)

!

asinus  Aug 9, 2017
#2
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If I don't mind asking. Other than addition theorm what other rules do I need to learn, that is in the same level of learning, concerning sin and cos.

I'm abit behind in mathematics. I think half-angle trigonetric formulae is one of them.

Guest Aug 9, 2017
#3
+7189
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Dear learner of trigonometry!

I wish you great success.

!

asinus  Aug 9, 2017

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