Show that `f(x)=cos(2x+pi/4)` is an increasing function on `(3pi//8,7pi//8)dot`

Explanation

To show that the function \( f(x) = \cos(2x + \frac{\pi}{4}) \) is an increasing function on the interval \( \left( \frac{3\pi}{8}, \frac{7\pi}{8} \right) \), we need to follow these steps:

### Step 1: Find the derivative of \( f(x) \)
To determine if the function is increasing, we first compute the derivative \( f'(x) \).

\[ f'(x) = \frac{d}{dx} \left( \cos(2x + \frac{\pi}{4}) \right) \]
...