While any point in the coordinate plane may be used as a point of reflection, the most commonly used point is the origin. In a point reflection in the origin, the image of the point x,y is the point -x,-y. Well it's pretty clear that a kept the same y coordinate but it's x coordinate was taken the opposite of so we're going to categorize this as reflection over the x axis excuse me y axis.
The final one that you should know by heart is xy is mapped onto yx. And the last thing is you can kind of consider this a flip that will be the non mathematical way of describing a reflection.
Here I have an original and I reflected this quadrilateral over this dotted little line onto the other side, so if we were to go in clockwise direction, after a I would have d after d I would have vertex c after vertex c I would have vertex b and after vertex b I would have vertex a.
Reflections in the coordinate plane: Reflect over the x-axis: When you reflect a point across the x-axis, the x-coordinate remains the same, but the y-coordinate is transformed into its opposite its sign is changed.
Notice that each point of the original figure and its image are the same distance away from the line of reflection.