Geometry Rotations
Goals Identify rotations in the plane. Apply rotation formulas to figures on the coordinate plane. 12/7/2017
Rotation A transformation in which a figure is turned about a fixed point, called the center of rotation. Center of Rotation 12/7/2017
Rotation Rays drawn from the center of rotation to a point and its image form an angle called the angle of rotation. G 90 Center of Rotation G’ 12/7/2017
A Rotation is an Isometry Segment lengths are preserved. Angle measures are preserved. Parallel lines remain parallel. Orientation is unchanged. 12/7/2017
Rotations on the Coordinate Plane Know the formulas for: 90 rotations 180 rotations clockwise & counter-clockwise Unless told otherwise, the center of rotation is the origin (0, 0). 12/7/2017
90 clockwise rotation Formula (x, y) (y, x) A(-2, 4) A’(4, 2) 12/7/2017
Rotate (-3, -2) 90 clockwise Formula (x, y) (y, x) A’(-2, 3) (-3, -2) 12/7/2017
90 counter-clockwise rotation Formula (x, y) (y, x) A’(2, 4) A(4, -2) 12/7/2017
Rotate (-5, 3) 90 counter-clockwise Formula (x, y) (y, x) (-5, 3) (-3, -5) 12/7/2017
180 rotation Formula (x, y) (x, y) A’(4, 2) A(-4, -2) 12/7/2017
Rotate (3, -4) 180 Formula (x, y) (x, y) (-3, 4) (3, -4) 12/7/2017
Rotation Example Draw a coordinate grid and graph: A(-3, 0) B(-2, 4) Draw ABC A(-3, 0) C(1, -1) 12/7/2017
Rotation Example Rotate ABC 90 clockwise. Formula (x, y) (y, x) 12/7/2017
Rotate ABC 90 clockwise. (x, y) (y, x) A(-3, 0) A’(0, 3) B(-2, 4) B’(4, 2) C(1, -1) C’(-1, -1) A’ B’ A(-3, 0) C’ C(1, -1) 12/7/2017
Rotate ABC 90 clockwise. Check by rotating ABC 90. A’ B’ A(-3, 0) C’ C(1, -1) 12/7/2017
Rotation Formulas 90 CW (x, y) (y, x) 90 CCW (x, y) (y, x) 180 (x, y) (x, y) Rotating through an angle other than 90 or 180 requires much more complicated math. 12/7/2017