Question

find integration of cosx /cos 3x dx

Answer 1

Step-by-step explanation:

I found: ∫cos(3x)dx=13sin(3x)+c

Explanation:

Considering:

∫cos(3x)dx=

we can set 3x=t

so: x=t3

and: dx=13dt

The integral becomes:

∫13cos(t)dt=13sin(t)+c

going back to x:

we know that t=3x:

=13sin(3x)+c