Differentiate w.r.t to' x 'using first principal, `cos(x^(2)+1)`

Explanation

To differentiate the function \( f(x) = \cos(x^2 + 1) \) with respect to \( x \) using the first principle of derivatives, we will follow these steps:

### Step 1: Define the function and the increment
Let \( f(x) = \cos(x^2 + 1) \). We need to find \( f(x + \Delta x) \):
\[ f(x + \Delta x) = \cos((x + \Delta x)^2 + 1) \]

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