Lines and Angles

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

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:

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...

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

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

If two angles are supplements, find the missing angle.