Question

Help please :
differentiate cos 2x ? how to solve this ?

Answer 1

is the answer -2sinx ?

Answer 2

Close, it's -2sin2x

Answer 3

Saying there are "two function."

Let f(x) be cosx and g(x) be 2x.

Apply chain rule: d/dx f(g(x)) = f'(g(x))·g'(x)

cos(2x) = -sin(2x) · 2 = -2sin(2x)

Is this clear?

Answer 4

ok i understand how we got -2sinx but how did we get 2x ?

Answer 5

ahhh ok i got it now !! thanks

Answer 6

do you mind if i ask you more questions ?

Answer 7

While applying chain rule, you derivative first function and left second function untouched, then derivative second function.

Answer 8

You're welcome. Close this question and post another question.