Finding area of a graph of x+y Hi so I am interested in finding the area of a graph given by this: 
$$\{(x,y)| 0 \leq x + y \leq \frac{1}{3}, \quad x\geq 0, \quad y\geq 0\},$$
graph between $0$ and $\frac{1}{3}$ for $x+y$, I've done a lot of calculus and integrations, but don't know where to start this this one. 
Any help would be appreciated. 

Draw the graph of the region $\{(x,y)| 0 \leq x + y \leq 1/3\}$.
Note that it would be a region between the two straight lines $x+y=0$ and $x+y=1/3$ and if you intersect it with the first quadrant( As $x,y>0$), you will get a triangle, whose area is $1/2\times 1/3\times 1/3=1/18$.
