Getting to Know Geometer’s Sketchpad - Triangles

Welcome too the Geometer’s Sketchpad, an exciting and useful tool for students of all ages. With Sketchpad, you can explore geometry in ways you never would be able to do otherwise. In this section, you will learn Sketchpad skills that you will use in doing activities and projects. Feel free to explore on your own.

1. Open Sketchpad. You should see this:



This is your “sketch pad.”

2. Go to the display menu and choose Preferences. Your screen should look something like this:



Make a check in the box next to Points. This will label your points as you go along.

3. Click OK to exit.

4. On the left side of the sketch you will see the toolbox. Each tool has a specific purpose that is summarized below.



You will learn how to use each of them in this first activity.

Draw a Triangle using the line segment tools.



Measuring the angles

Make sure that all three vertices are deselected. (Click in any white area to deselect. You should notice that nothing is highlighted.)

To measure Angle BAC:

• Highlight points B, A and C.

All three vertices should be highlighted. If you wish to unhighlight your points just click with the select in any white area on the pad.

• Choose angle from the Measure menu.

Note that if you move the point A (or B or C) the measurement for BAC will change accordingly.

Repeat for the other two angles.

Add Color to the triangle
Highlight the vertices of the triangle
Choose the selection tool. Click on and highlight the three vertices.

Make a triangle interior
With the three points highlighted, go to the construct menu and choose Polygon Interior.

Color it Red (or whatever other color you like)
At this time your triangle should be "shimmering". That means that it is highlighted. Right click your mouse and choose a color. Click in any white area to turn off the highlighting. You should see a colorful triangle.

Change the triangle by dragging each of the three vertices. What kinds of triangles can you make? Can you make all of these (below)?



· An Acute equilateral triangle
· An Obtuse Isosceles triangle
· A Right scalene triangle

Can you make an Obtuse Equilateral triangle? Why?
Can you make a Right Equilateral triangle? Why?

How do you know if you have made any of them? Use Sketchpad measuring tools!

Important Sketchpad Skills: Highlighting and Measuring Angles

Note on Highlighting
A very important thing in GSP is how to highlight objects. This is your way of telling the computer, "I'm talking about this object." To highlight you must use the select pointer tool. The computer tells you a straight object or a circle is highlighted by putting little black squares on the object. A point is highlighted when it looks a little larger and darker.