# I figured out the half angle just need help with the math

• Nov 24th 2012, 08:58 PM
M670
I figured out the half angle just need help with the math
Given http://webwork.mathstat.concordia.ca...d4cc3990b1.png and http://webwork.mathstat.concordia.ca...31d28e5821.png is in quadrant III, find the exact value of http://webwork.mathstat.concordia.ca...f43f6e9341.png.
Note: You are not allowed to use decimals in your answer. http://webwork.mathstat.concordia.ca...cee78702d1.png =
$\cos(\frac{\alpha}{2})=-\sqrt\frac{1+-(\frac{4}{5})}{2}$
I need help with the math after this??
• Nov 24th 2012, 09:10 PM
jakncoke
Re: I figured out the half angle just need help with the math
$1 - \frac{4}{5} = \frac{5 - 4}{5} = \frac{1}{5}$ bring the 5 down. You get $-\sqrt{\frac{1}{2 * 5 }}$
• Nov 24th 2012, 09:17 PM
M670
Re: I figured out the half angle just need help with the math
That worked perfectly
$-\sqrt\frac{1}{10}$ is just what I needed