Geometry Unit 5, sec 7.3
Rotations - guided notes
I) Rotations - sec. 7.3
A. Definition: A rotation is a transformation in which a figure is turned about a fixed point.
This point is called the center of rotation.
1. Rotation 90 degrees (counterclockwise): (x,y) maps to (-y,x).
Example: (4 , 1) becomes (-1 , 4)
2. Rotation 180 degrees (counterclockwise): (x,y) maps to (-x,-y).
Example:(4 , 1) becomes (-4 , -1)
3. Rotation 270 degrees (counterclockwise) or -90 degrees (clockwise): (x,y) maps to (y,-x).
Example: (4 , 1) becomes (1 , -4)
B. Rotational symmetry: a figure has rotational symmetry if the figure can be mapped onto itself by a rotation of 180 degrees or less.
Example: A circle, Square, Rhombus, Equilateral Triangle, and more. Any regular polygon with center angle 180 degrees or less.
An example of a figure without rotational symmetry: trapezoid
