Central symmetry is when every part of the original object has a matching point on the image, and the image is the same distance from a fi xed point but in the opposite direction. The image looks the same as the object, just upside-down and back-to-front. Image 1 on the right is the result of central symmetry of the object in the fi xed point O, the origin (0, 0).
y Object
6 9
5 8
4 7
3 2 1
–10–9–8–7 –5–4 –3–2 –1 –6
–2 –3
Fixed point Fixed point –10 1 2 3 4 5 6 7 8 9 10
–4 –7
–5 –8
–6 –9
4. Rotation
A rotation is the motion of a fi gure by holding one point fi xed as the centre and turning the fi gure by a certain angle in a particular direction.
A rotation turns a shape through a clockwise or anti-clockwise angle about a fi xed point known as the centre of rotation. The yellow, green and red images below are all diff erent rotations of the purple object around the origin (0, 0).
90 ° clockwise rotation y
5
4 3 2 1
–5 –4 –3 –2 –1 0 –1
–2 –3
–4 –5
C
180 °clockwise rotation y
5 A
90° 1
A' B' C' 2 B 3 4 5 C' x B' A'