How would the equation be written for the nth derivative? I understand it will be different for odd dertivatives and even derivatives. I'm working on f(x)= sin (3x) and I cannot figure out how to write the equation to the nth derivative. f'(x) = 3cos(3x) 1st derivative f"(x) = -9sin(3x) 2nd derivative f"'(x) = -27cos(3x) 3rd derivative f""(x) = 81sin(3x) 4th derivative. so for the odd nth derivatives of f(x), I have come up with something like: (-1) 3^n cos(3x) and for the even nth derivatives of f(x), I have come up with something like: (-1) 3^n sin(3x) but it's just not right. How do I get alternating signs in this formula?