I would like to know if I am doing these correctly. I am supposed to find exact solutions of pi/6,pi/4 for these problems.

cos(11pi/12), tan(pi/12), sin(5pi/12) This is one of the ones I did.

Cos(11pi/12)= Cos(3pi/4 + pi/6) - Sin(3pi/4 + pi/6)

Cos(3pi/4) Cos(pi/6) - Sin(3pi/4) Sin(pi/6)

-sqrt(2)/2 *sqrt(3)/2 - Sqrt(2)/2 *1/2 = -sqrt(6)/2 -sqrt(2)/2

Also if this is correct, do I use cotangent with tan.

Thank you,

Keith Stevens