46. In the Cartesian coordinate system, the coordinates of points $A, B$ are $(-1,-2),(2, a)$, respectively, and the distance between points $A, B$ is 5, then $a$ equals . $\qquad$
Answer: 2 or -6.
Solution: By the distance formula between two points, we get
$$
[2-(-1)]^{2}+[a-(-2)]^{2}=5^{2}
$$

Solving, we get
$a=2$ or -6.