Defining the cosine function

Click and drag the angle α to any value between 0° and 90°. Then click and drag b and b' to make any 2 right-triangles you want with angle α.

• Look at first triangle: Divide the length of the side adjacent to the angle α by the length of the hypotenuse. Write this number down.

• Look at the second triangle and again divide the length of the side adjacent to the angle α by the length of the hypotenuse. It should be the same number!

This is the value of cos(α).

 Sorry, the GeoGebra Applet could not be started. Please make sure that Java 1.4.2 (or later) is installed and active in your browser (Click here to install Java now) Extra check: Double-click on this worksheet to open it. Pick an angle α and find cos(α). Use the Move drawing pad tool to get an empty space on the worksheet. Then draw 2 points anywhere - not even on the same horizontal (but not too far apart). Use these 2 points to draw a right-triangle with angle α. Divide the length of the side adjacent to α by the length of the hypotenuse of this triangle. You should get the value of cos(α). LFS, Created with GeoGebra 