Problem:
The figure below shows line with a regular, infinite, recurring pattern of squares and line segments.
How many of the following four kinds of rigid motion transformations of the plane in which this figure is drawn, other than the identity transformation, will transform this figure into itself?
-
some rotation around a point of line
-
some translation in the direction parallel to line
-
the reflection across line
-
some reflection across a line perpendicular to line
Answer Choices:
A.
B.
C.
D.
E.
Solution:
Statement is true. A rotation about the point half way between an up-facing square and a down-facing square will yield the same figure.
Statement is also true. A translation to the left or right will place the image onto itself when the figures above and below the line realign (the figure goes on infinitely in both directions).
Statement is false. A reflection across line will change the up-facing squares to down-facing squares and vice versa.
Finally, statement is also false because it will cause the diagonal lines extending from the squares to switch direction.
Thus, only statements are true.
The problems on this page are the property of the MAA's American Mathematics Competitions