# What is the range of the function y = cos x?

The range of a function is all possible output, or $y$, values. The range of $y = \cos x$ is from -1 to 1.
In interval notation, the range is [-1,1] * Note that square brackets [ ] are used because because $y = \cos x$ can actually equal -1 and 1 ( for example, if you plug in $x = \pi$, $y = - 1$).
You can see visually in a graph that $y = \cos x$ can only equal values between -1 and 1 on the $y$-axis, hence that it is why it is the range. The doimain, however, is all real numbers. You can see that you can plug in all sorts of $x$ values, no matter how infinitely small and infinitely large they are- But you will always get a $y$ value with the restriction of [-1,1]