1. Section 3 – Trig Functions on the Unit Circle
Chapter 5
Section 3 – Trig Functions on the Unit Circle

2. The Unit Circle
Is it okay that any point (x,y) on the circle can be replaced with (cost,sint)?
How can we rewrite the other four trig functions using x and y?

3. Examples
Use the unit circle to find the following values. Numbers are in degrees.
EX 1: cos(-180)
EX 2: sec(90)
EX 3: tan(270)

4. More Examples
EX 4: Use the unit circle to find the values of the six trig functions for a 135 degree angle.

5. What if it’s not the Unit Circle?
What if we’re dealing with triangles that don’t have a radius of 1 (not on the unit circle)?
Well, we can use the same formulas that we already established, just with a different radius.

6. More Examples
EX 5: Find the values of the six trigonometric functions for angle Ѳ in standard position if a point with coordinates (5,-12) lies on its terminal side.
EX 6: Suppose Ѳ is an angle in standard position whose terminal side lies in Quadrant III. If sin Ѳ = -4/5, find the values of the remaining five trig functions of Ѳ.

7. Assignments
Chapter 5, Section 3
pgs #14-24E,34-38E,48