"(sigh) Geometry: the study of mathematical shapes and their relationships Geography (where you posted this): The study of natural features and political divisions"

Since you just said A = (2,3), I think you probably mean "what's A'"? The simplest way to figure that out is to take a piece of graph paper (you can make some yourself using lined paper and drawing vertical crossbars) and drawing the X and Y axes, graphing your triangle and then graphing its reflection. That should allow you to see where A' is situated.