Derivative Problem

[I'm]

Homework Statement

What's the 39th derivative of cosx?

Homework Equations

1st dy/dx: -sin x
2nd: -cosx
3rd: sinx
4th; cosx

The Attempt at a Solution

So it repeats every 4
so I used 39/4 and for a remainder of 3 so is is the 3rd one down?

I got sin x but I don't know if that's the way its supposed to be done ( the remainder is the number of derivative the answer is)

 

[temaire]

Yes, this is the way it should be done.

 

[lanedance]

sounds reasonable to me