What is the cos and sin of (13pi/3)? Also what is the reference angle in radians?

There are 2pi radians in a revolution.  Each time you do a whole revolution the sine value starts again.

 

sin(2pi + x) is the same as sinx

sin (4pi + x) is also the same as sinx

 

so sin    (13pi/3)  is the same as sin?

 

Answer this first.