# Thread: Sorry, I kinda hav a ton of ?'s, so here's another one... plez and thanks again

1. ## Sorry, I kinda hav a ton of ?'s, so here's another one... plez and thanks again

The exact value of sin 22.5 deg. is (sq root of a - (sq.root b)) / c. Find a, b, and c.

2. Originally Posted by Luckegrl_16
The exact value of sin 22.5 deg. is (sq root of a - (sq.root b)) / c. Find a, b, and c.
Using the half-angle formula:

$\sin{\frac{A}{2}} = \sqrt{\frac{1-\cos{A}}{2}}$

$\sin{\frac{45}{2}} = \sqrt{\frac{1-\cos{45}}{2}}$

$=\sqrt{\frac{1-\frac{\sqrt{2}}{2}}{2}}$

$=\sqrt{\frac{2-\sqrt{2}}{4}}$

$=\frac{\sqrt{2-\sqrt{2}}}{2}$

i.e, a = 2, b = 2, c = 2

Do not spam posts all over the board, or you're likely to be banned.

3. ## thanks

and thanks for the spam tip, i don't really use these things so ya

4. Well, feel free to post your problems if you have a lot, but don't post the same one in different forums.

Anyhoo, welcome to Mathhelpforum