How do you differentiate k(x)=-3 cos x?

1 Answer
Oct 26, 2016

You could start off by saying that:

y=k(x)

If this is the case:

y=-3cosx

-1/3*y=cosx

Now from here you can use implicit differentiation to get (dy)/(dx).

-1/3*(dy)/(dx)=-sinx

Which means that:

(dy)/(dx)=3sinx

And this means that:

k'(x)=3sinx

Realistically speaking, if you are studying differentiation, you've got to memorise:

If f(x)=cosx, f'(x)=-sinx.

This is very important.