Let me try:
|x| + |y| = a;
The question is to find the area of the figure that is formed by this equation.
To start with, we need to break the above down into all possible forms. As you can see, by putting + and - signs before x and y, we get 4 possible equations.
1. x + y = a;
2. x - y = a;
3 -x + y = a;
4. -x -y = a;
Further, these all fall into the form of y=mx + c (the equation for a straight line). Also note that lines 1 and 4 are parallel and lines 2 and 3 are parallel by virtue of having the same slope.
Next, find out where these lines hit the x and y axes.
1. (0,a) and (a, 0)
2. (0, -a) and (a,0)
3. (0, a) and (-a,0)
4. (0, -a) and (-a, 0)
If you plot the points above, you can see its a square, where half the diagonal is of length a.
From here you can find the area of the square.