Find the derivative of `cos x` at x=0.

Explanation

To find the derivative of \( \cos x \) at \( x = 0 \), we can follow these steps:

### Step 1: Define the function
Let \( y = \cos x \).

### Step 2: Find the derivative
To find the derivative \( \frac{dy}{dx} \), we differentiate \( y \) with respect to \( x \):
\[
...