Line Symmetry

Bellwork: REVIEWHappy Hal offered Joshua a job. Hal said that Joshua would make $500 commission for every $7500 in sales. Jolly Joe offered Joshua a job making $300 commission for every $5000 in sales. Which offered Joshua the better commission rate?BellworkTinas scar needs to be repaired. An auto-repair shop charges Tine $42.30 for replacement parts and $22.50 per hour (h) of labor. The final cost is $109.80. Tina writes the equation is the box.

How many hours of labor were spent on the repair?a. 5 hrsb. 4 hrsc. 3 hrsd. 2 hrs

Daily ActivitiesTSDHW REVIEWSymmetry:A Visual Presentation

DeSoto Central Middle School

Pre-AlgebraMrs. Yow

4Line SymmetryShape has line symmetry when one halfof it is the mirror image of the other half.

Symmetry exists all around us and many people see it as being a thing of beauty.

5 How would you define the term 'line symmetry'? Why might some people see line symmetry as a thing of beauty?

Is a butterfly symmetrical?

Line Symmetry exists in nature but you may not have noticed.At the beach there are a variety of shells with line symmetry.

Under the sea there are also many symmetrical objects such as these crabs

and this starfish.

9This type of symmetry is also called reflectional symmetry as the two parts reflect/match along each side of a dividing line ( or axis ).

Animals that have Line Symmetry Here are a few more great examples of mirror image in the animal kingdom.

THESE MASKS HAVE SYMMETRY These masks have a line of symmetry from the forehead to the chin. The human face also has a line of symmetry in the same place.

Human Symmetry The 'Proportions of Man' is a famous work of art by Leonardo da Vinci that shows the symmetry of the human form.

12There are also many examples of symmetry inside the human body e.g. the lungs, the kidneys, the brain, the skull, etc.

REFLECTION IN WATER If an object is reflected in water it is considered to have line symmetry along the waterline.

The Taj Mahal

Symmetry exists in architecture all around the world. The best known example of this is the Taj Mahal.

14In this view of the building there is a line of symmetry through the centre of the tomb from top to bottom.It was completed in 1630 by the Indian ruler Shahs Jahan as a tomb for his favourite wife Mumtaz Mahal who died as a result of giving birth to their 14th child. To build this tomb it took 20 000 workers, 20 years (Encarta 97) and it is rumoured that they used 40 000 elephants to transport the materials.

This photograph shows 2 lines of symmetry. One vertical, the other along the waterline.

(Notice how the prayer towers, called minarets, are reflected in the water and side to side).

2D Shapes and SymmetryAfter investigating the following shapes by cutting and folding, we found:

an equilateral triangle has 3 internal angles and 3 lines of symmetry.

a square has 4 internal angles and 4 lines of symmetry.

a regular pentagon has 5 internal angles and 5 lines of symmetry.

a regular hexagon has 6 internal angles and 6 lines of symmetry .

a regular octagon has 8 internal angles and 8 lines of symmetry.

21Is there a pattern here? How could you prove that a square really does have 4 lines of symmetry and not 2. A rectangle has 4 lines of symmetry. True or False? How could you prove it? What pattern can you see emerging on this page?

ClosureWhat can we determine is the general rule for estimating the number of lines of symmetry for a regular polygon?Lines of symmetry is about = the number of sides22