Geometry Section : 11.8 Rotations
Algebra Problem of the Day: Graph.
x ­ 2
y = 4
3
2x ­ 5y = ­10
Oct 2­7:11 PM
Today's Essential Question: Identify Rotations and Rotational Symmetry
Opener: What two transformations have we talked about so far?
Oct 2­7:18 PM
1
Concept 1: Identifying Rotations
Rotation
A rotation is a transformation in which a figure is turned about a fixed point.
The fixed point is the center of rotation.
The rays drawn from the center of rotation to a point and its image form an angle called the angle of rotation.
Oct 2­7:20 PM
Ex. 1:
Step 1 Step 2 (You will need a protractor and ruler.)
Oct 2­7:26 PM
2
Step 3 Oct 2­7:30 PM
Ex. 2: On Graph Paper
Oct 2­7:32 PM
3
Solution Oct 2­7:33 PM
You try! Checkpoint Exercise #4 p. 635
Solution Oct 2­7:35 PM
4
Concept 2: Rotational Symmetry
Rotational Symmetry
A figure in a plane has rotational symmetry if the figure can be mapped onto itself by a rotation of 180 or less.
A rectangle can be mapped onto itself in a clockwise or counterclockwise direction 180 about its center.
Oct 2­7:36 PM
Ex. 1: Does a Regular Hexagon have Rotational Symmetry? If so, describe the rotations that map the figure onto itself.
Oct 2­7:43 PM
5
Ex. 2: Does a trapezoid have rotational symmetry? If so, describe the rotations that map the figure onto itself.
Oct 2­7:52 PM
Now try the Checkpoint Exercises #1­3 p.
Oct 2­8:06 PM
6
Closure: Mini­Quiz
1. Rhombus
2. Isosceles Trapezoid
3.
Solution 1
Solution 3
Solution 2
Oct 2­8:12 PM
Learning Opportunity
p. 636­639 #1­12, 17­21 odd, 22­26, 37, 38
Oct 2­8:19 PM
7