Evaluate `|[1,x, y],[1,x+y, y],[1,x,x+y]|`

Explanation

To evaluate the determinant \( |[1, x, y], [1, x+y, y], [1, x, x+y]| \), we will follow these steps:

### Step 1: Write the Determinant
We start with the determinant:
\[
D = \begin{vmatrix}
1 & x & y \\
1 & x+y & y \\
...