Asked by JD

I did post it wrong.
sin(4x)/sin(x)=4cos(x)cos(2x).
Verify the identity, please explain!

Answers

Answered by Ms. Sue
Please, keep the same name when posting on Jiskha.

Answered by drwls
It has already been explained. See Reiny's answer to your previous post.
Answered by MathMate
For the left hand side, use
sin(4x)=2sin(2x)cos(2x)
sin(2x)=2sin(x)cos(x)
cos(2x)=cos²(x)-sin²(x)
and finally to eliminate sin²(x), use
sin²(x)=1-cos²(x)

For the right hand side, use
cos(2x)=cos²(x)-sin²(x)
and
sin²(x)=1-cos²(x)

Both sides will be expressed in terms of cos(x).

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