Question

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

Answer 1

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