I have an exam tomorow and I ran in to some problems with the following questions:

1. 2sinxcos^3x - 2sin^3xcox

and

2. Develop a forumula for sin3x in terms of sinx

Thanks in advance.

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- Jun 18th 2008, 01:47 PMandymacTrigonometry Identities
I have an exam tomorow and I ran in to some problems with the following questions:

1. 2sinxcos^3x - 2sin^3xcox

and

2. Develop a forumula for sin3x in terms of sinx

Thanks in advance. - Jun 18th 2008, 02:24 PMTKHunny
2sinxcos^3x - 2sin^3xcox

Factor

$\displaystyle 2\sin(x)\cos^{3}(x) - 2\sin^{3}(x)\cos(x)\;=\;2\sin(x)\cos(x)[\cos^{2}(x)-\sin^{2}(x)]$

Both those pieces (inside and outide the []) should look**very**familiar.

Quote:

2. Develop a forumula for sin3x in terms of sinx

That's almost all you need. - Jun 18th 2008, 02:25 PMMooQuote:

2. Develop a forumula for sin3x in terms of sinx

Thanks in advance.

$\displaystyle \sin(a+b)=\sin a\cos b+\sin b\cos a$

And then, you will need these formulae :

$\displaystyle \cos 2x=1-2 \sin^2x$

$\displaystyle \sin 2x=2 \cos x \sin x$

$\displaystyle \cos^2x=1-\sin^2x$