# Can someone show me how to use the half angle formula?

• Nov 20th 2006, 02:03 PM
qbkr21
Can someone show me how to use the half angle formula?
Thanks
• Nov 20th 2006, 04:08 PM
ThePerfectHacker
Quote:

Originally Posted by qbkr21
Thanks

You have that,
$\sin^2 x=\frac{1-\cos 2x}{2}$

$\cos^2 x=\frac{1+\cos 2x}{2}$

So to get your value for $\sin x,\cos x$ you take the square root. CAREFUL, since there are two roots it can be negative or positive. How do you know? Simple, determine the quadrant of the angle and where it lies.