# Cos(x) & Unit Circle - Radians

- Author:
- Linda Fahlberg-Stojanovska

- Topic:
- Circle, Cosine, Unit Circle

First notice the unit circle has a radius of 1.
Click and drag the slider for α. Note the size of α in degrees and in radians. (Although we wrote the word radians, it should NOT be written. There is no unit with radians.)
The ANGLE α is on the x-axis. The ANGLE α is the LENGTH OF THE ARC in the unit circle for the angle α in degrees. Read this sentence until you understand it. It is critical.
The x-coordinate of the point T , i.e. the base of the triangle is the value of the cosine function of the angle α.

Rounded to 3 decimal places, how much is α= ? What is size of α in degrees? Which is on the x-axis of the function in the graph above?
Rounded to 1 decimal place, how much is α= ? What is the size of α in degrees? Which is on the x-axis of the function in the graph above?
What is the height at the point when α= ? So what is ? Find this point on the graph of the function.
What is a decimal approximation for the coordinates of this point? Can you see that the scale of the graph is 1:1?
(I use the points (0,1) and (1.5,0) as my approximation when drawing the first half cycle of cos(x). Can you see why?)