Page 2 - Lesson Notes

For example, when point P with coordinates (5,4) is reflecting across the X axis and
mapped onto point P’, the coordinates of P’ are (5,-4). Notice that the x-coordinate
for both points did not change, but the value of the y-coordinate changed from 4 to -
4.

Definition: Reflection over the Y- Axis

A reflection of a point, a line, or a figure in the Y axis involved reflecting the image
over the Y axis to create a mirror image. In this case, the Y axis would be called the
axis of reflection.

When a point is reflected across the Y-axis, the Y-coordinates remain the same. But the X-
coordinates are transformed into its opposite signs.
Therefore, the reflection of the point (x, y) across Y-axis is (-x, y).

For example, when point P with coordinates (5,4) is reflecting across the Y axis and
mapped onto point P’, the coordinates of P’ are (-5,4). Notice that the y-coordinate
for both points did not change, but the value of the x-coordinate changed from 5 to -
5.

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