Composition of
Reflections
|
This exercise
will teach what happens to a figure when it is reflected across two different
intersecting mirror lines |
Instruct students to work through the above exercise. Ask them to describe in their own words,
based on their experience, a composition
of two reflections across two different intersecting mirrors. In addition, a relationship between the angle
formed by the mirrors and the rotation angle should be established. Answers should be compared and discussed in
class. This discussion will provide an
opportunity for the teacher to do the following demonstration.
• Obtain two 12 in. x 12 in. mirrors that
are hinged in the middle.
• Place a piece of making tape with a
classmates name spelled out in a corner of one of the mirrors.
• As the name is reflected in the other
mirror it appears to be written backwards.
• As the reflection of the backwards name
is reflected in the mirror with the masking tape, the name is no longer backwards. (a real example of a composition of two
reflections)
The conclusion of this discussion should end with the
establishment of a working description of this geometric concept.
A
composition of two reflections across two different mirror lines is a rotation
and the resulting angle is twice the angle between the two reflection axes.