Sine and cosine can be interpreted in multiple ways, such as the relationship between angles and side lengths in triangles, and as the coordinates of points on the unit circle. Since sine and cosine return exactly one output value for every input angle, they can also be interpreted as functions. Sine and cosine can be evaluated for any value of $x.$ Thus, their domain is all real numbers. Every output, however, ranges from $\text{-}1$ to $1$ — the range of both functions is $\text{-}1\le y\le 1.$