If we trace the values of sinθ and cosθ with θ on the x-axis, we find their sinusoidal graphs:

Looking at them more closely:

Notice that both sinx and cosx have a domain of x∈R and a range of (−1,1). The range is a consequence of the fact that these values come from coordinates on a unit circle, which are always between −1 and 1.

Notice also that cosx "lags" behind sinx by 2π​. Mathematically we can write