1. The problem asks for the range of the cosine function defined as $y = \cos x$. 2. The cosine function is a trigonometric function that outputs values based on the angle $x$ (in radians or degrees). 3. The formula for cosine is $y = \cos x$, where $x$ is any real number. 4. Important rule: The cosine function oscillates between -1 and 1 for all real values of $x$. 5. This means the minimum value of $\cos x$ is -1 and the maximum value is 1. 6. Therefore, the range of $y = \cos x$ is all values $y$ such that $$-1 \leq y \leq 1$$. 7. In plain language, the cosine function never outputs values less than -1 or greater than 1, it stays within this interval for all inputs. Final answer: The range of $y = \cos x$ is $$[-1, 1]$$.