Lesson 22 — Activity 3: Right-Angled Triangles


Getting Ready


In this activity, you will look closely at another triangle: the right-angled triangle.


A right-angled triangle has one angle that is exactly 90 degrees.


You will also watch a video and learn about scalene triangles, isosceles triangles, and equilateral triangles.


Think about This:


Can you see the right-angled triangles in this image?


    The sails of this boat are right-angled triangles.
Image courtesy of www.imagesgoogle.com



Let's look at right-angled triangles first. Remember that a right angle is an angle of exactly 90 degrees. A right-angled triangle has one angle that is exactly 90 degrees. This may be shown by putting a small square in the corner that is the right angle. Look at the triangle below.


This image shows a right-angled triangle.


Notice that the lower left-hand corner has a small square in it. This shows that this is a right angle.


There is a very quick way to draw a right angle. All you do is take a piece of paper, fold one corner over at an angle, draw two lines around the corner of the paper, unfold the paper, and draw the third line of your triangle. Where you drew the lines around the corner of the paper is a right angle.


Digging Deeper

Now watch this video, which reviews the triangles learned about in this lesson and also gives information on other triangles.



Digging Deeper

Just before you complete a final assignment in this lesson, click here to try this game to identify the different types of triangles.