Geometry

Lesson 6.3: Rotations

Notes

• A rotation uses a fixed point to turn a figure around, or about.
• The fixed point is called the center of rotation, or pivot point.
• The angle of rotation is the angle formed by lines connecting the pre-image to the center and the image to the center.

• Rotations in the coordinate plane

1. Rotation 90° counter-clockwise about the origin

• Switch coordinates and make the point fit the quadrant.

2. Rotation 90° clockwise about the origin         [or 270o CCW]        

• Switch coordinates and make the point fit the quadrant.

3. Rotation 180° about the origin

• Leave coordinate order alone, but make both of them the opposite sign.                

• IF YOU ARE NOT GIVEN A DIRECTION, ASSUME TO GO COUNTER-CLOCKWISE.

• A figure has rotational symmetry if it can be rotated onto itself, using its center as the center of rotation, in 180° or less in either direction.

1. 90° clockwise

2. 90° counter-clockwise
   

3. 180°

4. 270° clockwise