The diagrams here in Dave’s Short Trig Course are illustrated with a Java applet so that you can change the shapes of the figures.
If your browser is Java-enabled, and nearly all browsers are now, you can drag the points around in the diagrams and the diagram will adjust itself. What happens to the diagram when you drag the points around depends on what kind of point you’re dragging.
Free points are red. The free points, colored red, can be freely dragged about, and as they move, the rest of the diagram (except the other free points) will adjust appropriately. In the diagram above, the center of the circle is red, so it’s a free point. Try moving it around.
How to reset the diagram. If you’ve made some changes to the diagram, but then decide you want to reset it to the initial diagram, then click your mouse anywhere on the diagram to select the diagram, then type “r” or the space key, and the diagram will be reset to its initial position.
Sliding points are orange. Sliding points, colored orange, can be dragged about like the free points, except their motion is limited to either a straight line or a circle, depending on the point. In the diagram above, there are two sliding points. One sliding point is directly to the right of the center of the circle, and it slides along a horizontal line. Try moving it. You’ll see that the size of the circle changes.
The other sliding point slides along the circle, and it changes the size of the angle. Try sliding it around. The lines whose lengths are the sine, cosine, tangent, and cotangent all move. The meaning of these trig functions is described on various pages of this short course. Note what happens when the angle becomes obtuse or becomes a negative angle.
Other points. Most of the other points are colored black, and usually you can move them, too, and the entire diagram slides along with the point.
Pivot points are green. A few diagrams have “pivot points” specified. If a diagram has a pivot point, then the entire diagram shifts as you drag it, but when you drag a black point, then the diagram will rotate about the pivot point.
How to rip the diagram off the web page. Sometimes you would like to expand the diagram beyond its window on the web page. You can type “u” or press return, and the figure will be lifted off the page into a separate window. Note that you can resize the floating window as large as you like. Later, if you type “d” or press return again, while that window is selected, then the diagram is returned to the web page. Note that you can resize the floating window to make the diagram as large as you like.
Printing the pages. Note that most web browsers do not allow printers to print images created by Java applets. If you want to print the images, turn off Java in your browser. Then the plain images that appear can be printed.
For more information about the Java applet see the Geometry Applet.