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Bellwork. Pannini’s Pizza Parlor advertises that you could get a one-topping pizza from them once a week for over two years and never have exactly the same pizza twice! Are they correct? Here is their menu

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Bellwork

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## Bellwork

Pannini’s Pizza Parlor advertises that you could get a one-topping pizza from them once a week for over two years and never have exactly the same pizza twice! Are they correct? Here is their menu

How many triangles are there in the 4, 5 and 6th triangles if there are 1 in the first, 3 in the second and 6 in the third?

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## Bellwork Solution

Pannini’s Pizza Parlor advertises that you could get a one-topping pizza from them once a week for over two years and never have exactly the same pizza twice! Are they correct? Here is their menu

## Bellwork Solution

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How many triangles are there in the 4, 5 and 6th triangles if there are 1 in the first, 3 in the second and 6 in the third?

## Lines of Symmetry

Section 5.α

### The Concept

• Today we’re going to be talking about a relatively basic topic, but one that is very important to our discussion of geometry, specifically in regards to areas and three dimensional solids

Line of Symmetry

-Imaginary line drawn that creates a reproduced piece of an object

## Symmetry

• There are primarily two kinds of lines of symmetry

• Bilateral

• Splits the object exactly in half

• Reproduces a piece of the object as it rotates about a center

## Symmetry

Let’s take a closer look at rotational symmetry

Instead of splitting an object up we look to cut it into pieces from a “center of symmetry”

This is done in such a way that each piece replicates itself as it’s rotated around

## Symmetry

Typically there is at most two ways to divide an object radially, although there are many ways to do it bilaterally

## Examples

What are lines of symmetry for this object

## Example

What are bilateral lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What objects to we see on a daily basis that have lines of symmetry?

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

What are lines of symmetry for this object

## Example

This looks a lot like a reflection…

One of the ways that lines of symmetry are used is in the process of drawing objects

For instance

## Drawing

A helpful Theorem for us to remember governs symmetry in regular polygons

Theorem 5.20: Lines of symmetry in regular polygons

The number of lines of symmetry in a regular n-gon is equal to the number of sides

## Homework

9.6

1-20, 27-30 (don’t figure angles)

• Bilateral Symmetry

• Drawing using a line of symmetry