1. Section 4.1A Trigonometry (Degrees and Radians)
- Measurement of triangles

2. Rotation and Degree Measure
Terms:
Angle - determined by rotation of a ray about its endpoint

3. Initial side - starting position of the ray
Terminal side - position after rotation of the ray

4. Positive angles - generated by counter-clockwise rotation
Vertex - endpoint of the rays

5. Negative angles - generated by clockwise rotation

6. Ex 1: Find the degree measure of an angle represented by 2
Ex 1: Find the degree measure of an angle represented by 2.1 rotations counter-clockwise.
756º
Ex 2: Find the degree measure of an angle represented by 1.5 rotations clockwise.
-540º
Ex 3: Find the number of rotations for a degree of measure 1512º.
4.2 rotations counter-clockwise

7. Radian Measure
A central angle is an angle whose vertex is the center of a circle.
One radian is the measure of a central angle that
intercepts at arc whose length is equal to the
length of the radius of the circle.
1 revolution = 360° = 2π radians
180° = π radians

8. Conversion between degrees and radians
Since 360° = 2π radians and 180° = π radians the conversion that we use to convert from degrees to radians is:
Also, the conversion that we use to convert from radians to degrees is:

9. Ex 4: Convert the following degree measures to
radians (give answers in exact form).
a. 135º b. 540º
c º d. 400º

10. Ex 5: Convert the following radian measures to
degrees (round to the nearest 10th if necessary).
a b. 2
c d.

11. II I III IV Quadrants are labeled with Roman numerals
counter-clockwise from the top right. II I
III IV

12. Suggested Assignment:
Section 4.1A
pg 255 – 256
#5 – 8, 27 – 30, 45 – 64