1. Think of a x axis as a mirror line
2. So point A is currently two squares away from the mirror line so if your reflecting line AB over the x axis you would have to count two squares downwards to reflect point A over the line so by looking at the graph the precise coordinate of A(reflected) would be (1,-2)
3. Now do the exact same with point B and finally join the points together.
4. Furthermore if this question asked to reflect AB over the y axis all thats different is that you are treating the y axis as the mirror line.
I hope this made sense sorry if I failed to explain it well .