Draw the Cosine Curve (0 - 360 degrees)
In the circle above (which has radius 1), the vertical axis cuts the blue chord in half. As we change the value of the angle, the length of the half chord changes. The length of a horizontal half chord is the origin of the cosine function.
When , we see that the horizontal half chord has length 0.87.
We notice that in the first quadrant, this length is the same as the x coordinate of the point A.
We define the cosine of the angle as the x coordinate of the point A. Therefore, , (2 s.f.). Also, (2 s.f.).
The graph on the right maps the value of to the x coordinate of the point A. Notice the point .
Move the slider to see how cosine changes as the angle changes.