1. 7.1 Angles and Their Measure
MAT 204 SP09
7.1 Angles and Their Measure
In this section, we will study the following topics:
Terminology used to describe angles
Degree measure of an angle
Radian measure of an angle
Converting between radian and degree measure

2. Angles Trigonometry translated: _____________ of _____________
Angle Measure

3. Standard Position Vertex at origin
The initial side of an angle in standard position is always located on the positive x-axis.

4. Positive and negative angles
When sketching angles, always use an arrow to show direction.

5. We’ll start with degrees, denoted by the symbol º.
Measuring Angles
The measure of an angle is determined by the amount of rotation from the initial side to the terminal side.
There are two common ways to measure angles, in degrees and in radians. ******************************************************************
We’ll start with degrees, denoted by the symbol º.
One degree (1º) is equivalent to a rotation of of one revolution.

6. Measuring Angles

7. Acute and Obtuse Angles
Acute angles have measure between _____º and _____º.
Obtuse angles have measure between ____º and _____º.
Straight angles measure _______º.

8. Classifying Angles Example: 50º is a ____ quadrant angle.
Angles are often classified according to the QUADRANT in which their terminal sides lie.
Example:
50º is a ____ quadrant angle.
208º is a ____ quadrant angle II I
-75º is a _____ quadrant angle III IV

9. Classifying Angles
Standard position angles that have their terminal side on one of the axes are called QUADRANTAL ANGLES.
For example, 0º, 90º, 180º, 270º, 360º, … are quadrantal angles.

10. Sketching Angles (Degrees)
Sketch in standard position. In which quadrant is  located?
Sketch in standard position. In which quadrant is  located?

11. Complementary and Supplementary Angles
Complementary Angles
Two positive angles are complementary if their sum is ______º
Angles that measure 22º and 68º are complements.
Supplementary Angles
Two positive angles are supplementary if their sum is _______º
Angles that measure 137º and 43º are supplements.

12. Radian Measure Definition of Radian:
A second way to measure angles is in radians.
Definition of Radian:
One radian is the measure of a central angle  that intercepts arc s equal in length to the radius r of the circle.
In general, for  in radians,

13. MAT 204 SP09
Radian Measure

14. Radian Measure

15. Conversions Between Degrees and Radians
To convert degrees to radians, multiply degrees by
To convert radians to degrees, multiply radians by
Example
Convert from Degrees to Radians: 210º

16. Conversions Between Degrees and Radians
Example
a) Convert from radians to degrees:
b) Convert from radians to degrees: 3.8

17. Conversions Between Degrees and Radians
Try it!
c) Convert from degrees to radians (exact):
d) Convert from radians to degrees:

18. Conversions Between Degrees and Radians
Again!
e) Convert from degrees to radians (to 3 decimal places):
f) Convert from radians to degrees (to nearest tenth): 1 rad

19. Degree and Radian Form of “Special” Angles
0° 
360 ° 
30 ° 
45 ° 
60 ° 
330 ° 
315 ° 
300 ° 
 120 °
 135 °
 150 °
 240 °
 225 °
 210 °
 180 °
90 ° 
270 °  
Degree and Radian Form of “Special” Angles

20. Sketching Angles (Radians)
MAT 204 SP09
Sketching Angles (Radians)
Sketch in standard position. In which quadrant is  located?
Sketch in standard position. In which quadrant is  located?

21. Degrees, minutes, and seconds
MAT 204 SP09
Degrees, minutes, and seconds
1 minute (1’) = degree OR ° = ______ minutes
1 second (1”) = _____ minute = _____ degree OR 1’ = _____”
Example
Convert to decimal degrees:

22. Degrees, minutes, and seconds
Conversions between decimal degrees and degrees, minutes,
seconds can be easily accomplished using your TI graphing
calculator.
The ANGLE menu [ ] on your calculator has built-in features for converting between decimal degrees and DMS.
APPS
Note that the seconds (“) symbol is not in the ANGLE menu. Use  for “ symbol.

23. Practice Using your TI graphing calculator,
Convert to decimal degrees to the nearest hundredth of a degree.
Convert ° to an equivalent angle expressed to the nearest second.

24. MAT 204 SP09
End of Section 7.1