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:
$\displaystyle \sin{\frac{A}{2}} = \sqrt{\frac{1-\cos{A}}{2}}$
In your case,
$\displaystyle \sin{\frac{45}{2}} = \sqrt{\frac{1-\cos{45}}{2}}$
$\displaystyle =\sqrt{\frac{1-\frac{\sqrt{2}}{2}}{2}}$
$\displaystyle =\sqrt{\frac{2-\sqrt{2}}{4}}$
$\displaystyle =\frac{\sqrt{2-\sqrt{2}}}{2}$
i.e, a = 2, b = 2, c = 2
Do not spam posts all over the board, or you're likely to be banned.