The domain of this sine function is the entire set of real numbers. Since there is no real value of x for which sin(x) becomes undefined, then the entire set of reals is the domain.
(On the other hand, the range would be from -4 <= y <= 4, since the sine function can only have a value ranging from -1 to 1, and multiplying 4 expands that from -4 to 4.)
