Question 577644
{{{ sin( (13*pi)/12) }}}
{{{ (13*pi)/12 }}} = {{{ (12*pi)/12 + (1*pi)/12 }}}
{{{ (12*pi)/12 = pi }}}
{{{ pi + pi/12 }}} is in the 3rd quadrant where
the sine is negative
In degrees, {{{ pi/12 = 180/12 }}}
{{{ 180/12 = 15 }}} degrees
The answer is {{{ - sin(15) }}} 
( I don't have a calculator )