Evaluate `|(x, y, x+y),( y, x+y, x),( x+y, x, y)|`.

Explanation

To evaluate the determinant \( D = \begin{vmatrix} x & y & x+y \\ y & x+y & x \\ x+y & x & y \end{vmatrix} \), we will follow these steps:

### Step 1: Write the Determinant
We start by writing the determinant clearly:
\[ D = \begin{vmatrix} x & y & x+y \\ y & x+y & x \\ x+y & x & y \end{vmatrix} \]

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