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.