Given that the domain for sin x is the domain for sin 3x will be
Lets say that when you solve for sin x, you get x = for the domain
Now to find for 3x, this means 3 revolutions, that is,
1st revolution, x =
2nd revolution, 2x = , (where 2\pi radians is one revolution or 360 degrees.)
3rd revolution, 3x =
So this 3rd revolution, that is for 3x, would be for the domain
To find once again for x all you need to do is divide all the six answers that was found in the 3rd revolution by 3, ensuring that it now lies in the domain .