Reflection over the X Axis

Launch Geometer's Sketchpad.

Create a new sketch
Under graph in the menu

- select show grid
- snap points.

Using the line segment tool connect points
(-2,1)
(-7,2)
(5,5)
Use the selection tool and click outside the figure which you just created.
Using the selection tool, select each of the three points.
Under display on the menu, choose label points.
Double click the Y axis. This indicates to GPS that you are about to mirror your image over the Y axis.
Use the selection tool to select each of the three points and the three line segments.
Under transform on the menu choose reflect.
Use the selection tool to select the points on the new figure that you just created by reflecting your original figure over the Y axis.
Under display menu choose show labels. Notice that the new labels. The orginal point A now become A prime and the original points B and C also become B and C prime.
What happens to the value of the Y coordinate, when we reflect over the Y axis?

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