3. Given point $P_{1}(3, a)$ is symmetric to point $P_{2}$ $(b,-2)$ with respect to the $x$-axis, find the values of $a, b$ and the coordinates of the point $P_{1}$ symmetric to the $y$-axis and the origin.
(Ans: $a=2, b=3$;
$$
(-3,2) ;(-3,-2)) \text {. }
$$