Copy of Algebraic Method to find the rotation about a point
- Author:
- Jennifer Mayrovitz, rajiv
This material shows an algebraic method to find the rotation (90, 180, 270 anticlockwise) of a point A
about any point C which is not the origin.
Consider a point A rotated about the center C.
Step 1: We change A to A1=A-C
Step 2: We apply the rule for rotation of point A1 about origin to get A2
(a) 90 anticlockwise (x,y)->(-y,x)
(b) 180 anticlockwise (x,y)->(-x,-y)
(c) 270 anticlockwise (90 clockwise) (x,y)->(y,-x)
Step 3: We add C to get A3=A2+C
Finally, we observe that A, A1, A2 and A3 form a parallelogram.
By moving the slider, we can change the angle of rotation.
Move the point A or C.