Posted by Briana on Friday, April 13, 2012 at 3:17pm.
How do i find the exact value of sin 15 using the half angle formula

Trig  Damon, Friday, April 13, 2012 at 3:30pm
sin (30/2) = +/ sqrt [(1cos 30)/2]
+ in first quadrant
= sqrt [ (1  {sqrt 3}/2)/2) ]
= sqrt [ (2  sqrt 3)/4 ]
= (1/2) sqrt (2  sqrt 3)

Trig  Reiny, Friday, April 13, 2012 at 3:35pm
use
cos 2A = 1  2sin^2 A
cos 30° = 1  2sin^2 15°
√3/2 = 1 2sin^2 15°
2sin^2 15°  1  √3/2 = (2√3)/2
sin^2 15° = (2√3)/4
sin 15° = √(2√3) /2
it would have been easier to do
sin15°
= sin(45°30°)
= sin45cos30  cos45sin30
= (√2/2)(√3/2) (√2/2)(1/2)
= (√6  √2)/4 which yields the same result as above
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