# Math Help - More trig differentials

1. ## More trig differentials

Yeah I missed this lesson in class because my alarm never went off. So i have plenty of question por vous.

f(x) = cos^9(x^4)

not a clue

2. Chain Rule rules here!

$f'(x)=9\cos^8(x^4)\cdot(\cos x^4)'$

Can you take it from there?

3. got it! thanks!