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Trigonometry Easy Identity Question

tmt

Active member
Jan 15, 2014
236
Hi,

I just want to double check that

2cos(x)sin(x) = 2sin(x)cos(x) = sin(x)2cos(x) = sin(2x)

Thanks,

Tim
 
Last edited:

Evgeny.Makarov

Well-known member
MHB Math Scholar
Jan 30, 2012
2,492
Yes. the identity is correct. You can find a list of trigonometric identities in Wikipedia. See, in particular, double-angle formulas.

A couple of remarks about notation. One should write $\sin x$ (with a space) or $\sin(x)$, not sinx. If the argument is followed by another factor, then the argument should be wrapped in parentheses. For example, $\sin x\cos x$ can theoretically be parse either as $\sin(x)\cos(x)$ or as $\sin(x\cos(x))$, but $\sin(x)\cos(x)$ clearly shows that the argument of sine is just $x$.