9.3 Rotations : turning a figure about a fixed point (center of rotation)
A
P
B
C
Construction: Compass and protractor.
Rotate
o
ABC 120 about point P.
A
P
C
B
Rotational Symmetry (or Radial Symmetry): A figure has
rotational symmetry if it can be rotated about a point by an
angle greater than 00 and less than 3600 so that the image
coincides with the preimage.
magnitude of rotational symmetry: the smallest angle through
which a figure can be rotated to coincide with itself.
The number of times a figure coincides with itself as it rotates
through 3600 is called the order of rotational symmetry.
o
magnitude = 360
order
Determine whether each figure has rotational symmetry. If
yes, locate the center of symmetry, give the magnitude of
symmetry and the order of symmetry.
A three dimensional figure has symmetry about an axis if
there is a line about which the figure can be rotated (by an
angle greater than 00 and less than 3600 ) so that the image
coincides with the preimage.
Determine whether each figure has symmetry about an axis.