Solve `(dy)/(dx) = sec (x+y)`

Explanation

To solve the differential equation \(\frac{dy}{dx} = \sec(x + y)\), we will follow these steps:

### Step 1: Substitution
Let \( t = x + y \). Then, we can express \( y \) in terms of \( t \):
\[ y = t - x \]

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