Geometry Rotations
2/14/2016 Goals Identify rotations in the plane. Apply rotation formulas to figures on the coordinate plane.
2/14/2016 Rotation A transformation in which a figure is turned about a fixed point, called the center of rotation. Center of Rotation
2/14/2016 Rotation Rays drawn from the center of rotation to a point and its image form an angle called the angle of rotation. Center of Rotation 90 G G’
2/14/2016 A Rotation is an Isometry Segment lengths are preserved. Angle measures are preserved. Parallel lines remain parallel. Orientation is unchanged.
2/14/2016 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).
2/14/ clockwise rotation Formula (x, y) (y, x) A(-2, 4) A’(4, 2)
2/14/2016 Rotate (-3, -2) 90 clockwise Formula (x, y) (y, x) (-3, -2) A’(-2, 3)
2/14/ counter-clockwise rotation Formula (x, y) ( y, x) A(4, -2) A’(2, 4)
2/14/2016 Rotate (-5, 3) 90 counter-clockwise Formula (x, y) ( y, x) (-3, -5) (-5, 3)
2/14/ rotation Formula (x, y) ( x, y) A(-4, -2) A’(4, 2)
2/14/2016 Rotate (3, -4) 180 Formula (x, y) ( x, y) (3, -4) (-3, 4)
2/14/2016 Rotation Example Draw a coordinate grid and graph: A(-3, 0) B(-2, 4) C(1, -1) Draw ABC A(-3, 0) B(-2, 4) C(1, -1)
2/14/2016 Rotation Example Rotate ABC 90 clockwise. Formula (x, y) (y, x) A(-3, 0) B(-2, 4) C(1, -1)
2/14/2016 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(-3, 0) B(-2, 4) C(1, -1) A’ B’ C’
2/14/2016 Rotate ABC 90 clockwise. Check by rotating ABC 90 . A(-3, 0) B(-2, 4) C(1, -1) A’ B’ C’
2/14/2016 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.