The range of the cosine function is $[-1, 1]$.

This means that for any input $x$, the output of the cosine function will always lie between $-1$ and $1$, inclusive.

Would you like more details or have any further questions?

Here are 5 related questions to explore further:

1. What is the domain of the cosine function?
2. How is the period of the cosine function defined?
3. What is the amplitude of the cosine function?
4. How does the graph of the cosine function look over one period?
5. How is the cosine function related to the sine function?

Tip: The cosine function repeats its values every $2\pi$ radians, which is known as its period.