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).

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Extra check: Double-click on this worksheet to open it. Pick an angle α and find cos(α). Use the Move drawing pad tool MoveDP 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).

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