1. Radian Measure and applications
C2 Chapter 6

2. A radian An Intro
Look at this diagram- applet:

3. 1 Radian

4. A radian
Definition: if the circumference of a circle is 2пr how many r’s will go around the circle?

5. The relationship Yes 2  is equal to one full turn of a circle
So 2  = 360 0
Or it is easier to remember
 = 180 0

6. Complete this table Radians Degrees 3/4 c /2 c 90 /4 c 3 /2 c 1 c
270 0
150 0
120 0
330 0

7. Common angles
Click here

8. Arc length Do you want to see the proof or just the formula?
Length of an arc l = θ
Circumference п
The proportions are the same!
Since the circumference is 2пr
Then l = rθ
Remember the angle θ is in radians!

9. Area of a sector Area of sector A = θ area of circle 2п
Since the area of a circle is пr2
A = ½ r 2 θ
Please Remember to use RADIANS

10. Arc length, area of a sector
Area of a sector proof:
Arc length:
Please remember these angles in these two formulae are all in RADIANS!

11. Arc length
To find the arc length of a circle when the angle subtended is given in radians we use this formula:
Arc length = r  where r is the radius and  is the angle subtended in radians r

12. Radian Click here for a game Match here
Radian practice with trig functions here

13. Area of a segment
Remember another formula or remember the method using common sense?
Let’s use our common sense!
What steps would you have to take to find the area of the segment?

14. Finding the Area of a Segment
Please use Radians!

15. How do I find the area of a segment?
Look at the following diagram and follow the hint steps to find the area of the segment.
Shade in the segment in the circle below. Label the triangle AOB. Angle AOB = 0.5 radians and the radius is 12 cm.
Find the area of the sector
Find the area of the triangle using ½ absinC
What is the area of the segment?