Question 373947
{{{cos(8pi/3)}}}

{{{cos(expr(8/3)pi)}}}

{{{cos(expr(2&2/3)pi)}}}

{{{cos((2+2/3)pi)}}}

{{{cos(2pi+expr(2/3)pi))}}}

{{{cos(expr(2/3)pi+2pi)}}}

By the fact that the period of cosine is {{{2pi}}}, the above equals

{{{cos(   expr(2/3)pi  )}}}

and that's the same as {{{2pi/3}}} or 120°, a second quadrant
angle which has a cosine of

{{{-1/2}}}

Edwin</pre>