S1T1 Symmetry: Line and Rotational

Line symmetry

The LINE that divides a shape into 

.  two identical halves

.  fits exactly onto each other.

=> One half is mirror mage or reflection of the other 

      2 identical halves where one is the mirror image or reflection of the other

=> A shape with a line of symmetry has a symmetrical shape.

=> A shape can have more than 1 line of symmetry.

=> A shape with a line of symmetry has a symmetrical shape.

=> A shape can have more than 1 line of symmetry.

Rotational Symmetry

Rotate ~ Turn about an axis or a centre or point.

The object rotates at 1 point, and match the starting shape after the rotation.

Order of Rotational Symmetry

=> In turning the shape for 360 (for complete round), the number of times that the shape matches/map to the original shape.

Example

What is the rotational symmetry of the rectangle?

Step1

Place a mark/point on the rectangle, and rotate (turn).

Step 2

Stop and rotation when the position of the rectangle is the same as the original position => after turning 180

             => 1 order

Step3

Continue turning for the rectangle to be back to original position until it has rotated 360 => another 180 turning

       => order = 1 + 1 = 2

The rectangles 'matches' the shape at the start for 2 times when turning through 360 o (a complete circular motion).

Rectangle has rotational symmetry of order 2, at 180 o and 360 o

Practice

How many line of symmetry and rotational symmetry for the following objects?