trig
posted by jj reddick .
determine an exact expression for the trigonometric function sin(13pi/12).

note that 13pi/12 is also 195 degrees, which can be expressed as difference of two angles, 240  45:
sin(13pi/12) = sin(195) = sin(24045)
*expanding this,
sin(240)cos(45)cos(240)sin(45)
(sqrt(3)/2)(sqrt(2)/2)(1/2)(sqrt(2)/2)
(sqrt(6)/4)+(sqrt(2)/4)
therefore:
{[sqrt(2)sqrt(6)]/4}
so there,, :)