Lines and Angles

## Types of angles

This page shows the different types of angles and their names: acute, right, obtuse, straight, and reflex.

# What is the sum of the angles in a star?

We know the sum of the internal angles in a triangle is always 180°. We also know that the sum of the internal angles in a quadrilateral is always 360°. What about the sum of the angles in a five-pointed star?

For this investigation, create several different five-pointed stars. Then measure the internal angles of the five points. Record your measurements in a table. Use words, numbers, and pictures to clearly explain your findings.

Examples of stars:

## Angles in Polygons

Use this applet to investigate the sum of angles in polygons. Is there a pattern? Can you predict the sum of the angles in a 20-sided polygon?

Use the applet...

## Lines & Angles

This is the cover page for the Lines and Angles pages.

## Vertical Angles

What are vertical angles? This applet shows you.

## Why is the sum always 180°? (A different look.)

A different demonstration of why the sum of the angles in a triangle is always 180°.

## Sum of the angles in a triangle

What is the sum of the angles in ANY triangle?

## Supplementary Angles - the definition

What are supplementary angles? Use this applet to find out.

## Protractor Practice

Practice using a protractor with this applet.

## Supplementary Angles - find the missing angle

If two angles are supplements, find the missing angle.  