Osaka
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By First writing 3x = x + 2x

show that sin(3x) = 3sin(x) - 4sin^3(x)
Im not too sure how to do this question
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the bear
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your pic did not come out... but your name is visible.
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RDKGames
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(Original post by Osaka)
By First writing 3x = x + 2x

show that sin(3x) = 3sin(x) - 4sin^3(x)
Im not too sure how to do this question
Using that tip, you have \sin(3x)=\sin(x+2x)

For simplicity, let's say 2x=A

Then you have \sin(3x)=\sin(x+A)

Now you can apply the expansion for compound angles of sine.

Once that is done, you will have a \cos(A) and a \sin(A) which is just \cos(2x) and \sin(2x). Apply the double angle expansion on both and simplify fully.
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Osaka
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Thanx a lot!! That really helped - I forgot about the double angle rule
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