# Help Proving double-angle identities

• July 21st 2007, 12:36 AM
fam600
Help Proving double-angle identities
Can someone prove this for me, please show enough steps so that i know what your doing along the way. Thanks

sin3x=3sinx-4sin^3x - the x isn't with ^3.
• July 21st 2007, 01:20 AM
red_dog
$\sin 3x=\sin (2x+x)$ and use the formula
$\sin(a+b)=\sin a\cos b+\sin b\cos a$
and $\sin 2x=2\sin x\cos x, \ \cos 2x=1-2\sin^2x$