2. Let $A=\{a \mid-1 \leq a \leq 2\}$, then the area of the plane point set $B=\{(x, y) \mid x, y \in A, x+y \geq 0\}$ is $\qquad$ .
Answer: 7.
Solution: The point set $B$ is shown as the shaded area in the figure, and its area is
$$
S_{\text {MPQ }}-S_{\triangle Y R S}=3 \times 3-\frac{1}{2} \times 2 \times 2=7 \text {. }
$$