Posted by Adam on .
f(x)=8cos4x
What is the derivative? Im doing online homework and i keep getting an incorrect answer. How do you work out this problem correctly? thanks

calc 
Reiny,
you must know that if
y = a cos kx, where k is a constant, then
dy/dx = a(k)sin kx
so f(x) = 8cos 4x
f'(x) = 32sin 4x