Express as a function :

c.tan (810degrees + theta )

I'm confused between two answers .

1. that it would be tan 90 deg (which is undefined)

2. it would be cot theta

?? can you tell me what i should do to get the right answer.

can you correct the rest for me please?

Express each as a function of theta:

a. sin (270deg + theta)= cos theta
b. cos (pi + theta)= -cos theta
c. tan (810 + theta)= ?????
d. sin (theta - 180)= -sin theta