Question

What is the range of a cosine function?

Answer 1

The smallest y can be is y = -1. The largest it can be is y = 1. The value of y can be anything in between. The value of y is a real number.

Answer: Choice D) All real numbers between -1 and 1 including -1 and 1

Note: we can write that as $-1 \le y \le 1$ which in interval notation would look like $[-1, 1]$. The square brackets tell us to include the endpoints.