Example 2. Constructing polygons (with an introduction to dragging)
With segments we can construct more complicated shapes like polygons (simple closed curves). First, we construct the simplest polygon, a triangle. Open a New Sketch by selecting New Sketch under the File menu (select File and then New Sketch). We only need the STRAIGHTEDGE TOOL to construct a triangle. Select it. Now construct a segment (refer to Example 1 if necessary). Next, click again on one of the endpoints. You will notice that in version 4 the red dot is surrounded by a blue circle (Figure 5). If you use a Mac, the circle is red (again remember that no coloring occurs in older versions). Next, move to another place on the screen and click (this is the third vertex of the triangle). Construct segments to complete the triangle by clicking on the third vertex and then on the first vertex. One common mistake is to click close to the vertex but not on the vertex. One way to make sure that you are going to construct a segment with two vertices given (and not creating others) is by noticing two things. First, once the initial vertex is about to be selected, a blue circle surrounds it and the bottom left corner of the screen says "...from Point..." Then you can click on it. A similar situation happens when the ending vertex is about to be selected, however the bottom left corner of the screen says "...to Point." Once you see this comment, you can click on it. Label the vertices of the triangle.
Figure 5
Sometimes we need smaller or larger constructions than the ones we constructed originally. Here is one of the advantages of dynamic constructions over pencil-and-paper constructions. Instead of erasing everything and starting all over, we can drag the shape until it "looks" like the one we need or is an appealing construction. Click on the SELECTION ARROW TOOL, the top tool on the Toolbox. Click on any vertex of the triangle and while holding the mouse button down, move the mouse around the screen. Notice how two sides of the triangle stretch and the corresponding label of the vertex being dragged moves around.
Drag the vertices of your triangle until it "looks" like the triangle in Figure 6.
Figure 6
Your triangle does not need to look exactly like the one below, but similar. In a new sketch (in the File menu), use the directions above to construct polygons like the ones in Figure 7. Again, they do not need to be exactly the same, but similar.
Figure 7