section 1.1 angle measure and arc length section 1.1 angle measure and arc length
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Section 1.1Angle Measure and Arc
Length
Section 1.1Angle Measure and Arc
Length
Objectives:1. To draw an angle in standard
position.2. To convert between degree and
radian measure.3. To calculate arc length using
angle measure and radius length.4. To review the distance and
midpoint formulas.
Objectives:1. To draw an angle in standard
position.2. To convert between degree and
radian measure.3. To calculate arc length using
angle measure and radius length.4. To review the distance and
midpoint formulas.
An angle in standard position has the positive x-axis as its initial ray and the origin as its vertex.
An angle in standard position has the positive x-axis as its initial ray and the origin as its vertex.
DefinitionDefinitionDefinitionDefinition
Standard PositionStandard Position
initial rayinitial ray
terminal rayterminal ray
VV
CC
AA
BB CC
AA
6060
Standard PositionStandard Position
Standard PositionStandard Position
FF
GGEE -120-120
AA
CCBB
8080
Standard PositionStandard Position
Coterminal angles are angles in standard position with the same terminal ray.
Coterminal angles are angles in standard position with the same terminal ray.
DefinitionDefinitionDefinitionDefinition
Coterminal AnglesCoterminal Angles
AA
CCBB440440
AA
CCBB
8080
A radian is the measure of an angle formed by two radii of a circle so that the intercepted arc has a length equal to the radius of the circle.
A radian is the measure of an angle formed by two radii of a circle so that the intercepted arc has a length equal to the radius of the circle.
DefinitionDefinitionDefinitionDefinition
RadianRadian
BB CC
AA
mABC = 1 radian 57.3mABC = 1 radian 57.3
Whenever an angle measure is given without degrees specified as the unit of measure, it is measured in radians.
Whenever an angle measure is given without degrees specified as the unit of measure, it is measured in radians.
The unit circle has its center at the origin with a radius of one unit.
The unit circle has its center at the origin with a radius of one unit.
DefinitionDefinitionDefinitionDefinition
Unit CircleUnit Circle
BB CC
AA
(1, 0)(1, 0)
Convert between degrees and radians by setting up a proportion.
Convert between degrees and radians by setting up a proportion.
180180
ππ==
degdegmm
radradnn
In this proportion, substitute the known measure and solve for the other measure.
In this proportion, substitute the known measure and solve for the other measure.
Change 60 degrees to radians.Change 60 degrees to radians.
m degm degn radn rad
180180
==
Change 60 degrees to radians.Change 60 degrees to radians.
60 deg60 degn radn rad
180180
==
n(180) = 60n(180) = 60
n =n = 1.051.0533
Change 5.6 radians to degrees.Change 5.6 radians to degrees.
m degm degn radn rad
180180
==
Change 5.6 radians to degrees.Change 5.6 radians to degrees.
m degm deg5.6 rad5.6 rad
180180
==
5.6(180) = m5.6(180) = m
m =m = 320.9° 320.9°5.6(180)5.6(180)
EXAMPLE 1 Find the measure of in degrees and radians.EXAMPLE 1 Find the measure of in degrees and radians.
= ¼ of a circle
¼(360º) = 90º
¼ • 2 =
= ¼ of a circle
¼(360º) = 90º
¼ • 2 =22
Practice Question: Find the measure of in degrees.Practice Question: Find the measure of in degrees.
= ¾ of a circle
¾(360º) = 270º
= ¾ of a circle
¾(360º) = 270º
A quadrantal angle is an angle whose terminal ray lies on one of the axes.
A quadrantal angle is an angle whose terminal ray lies on one of the axes.
DefinitionDefinitionDefinitionDefinition
Quadrantal AngleQuadrantal Angle
BB CC
AA
90°90°
BB CC
AA
180°180°
Quadrantal AngleQuadrantal Angle
BB CC
AA
270°270°
Quadrantal AngleQuadrantal Angle
BB CC
AA
360°360°
Quadrantal AngleQuadrantal Angle
Concentric circles have the same center but different radii. A central angle is an angle having its vertex at the center of a circle.
Concentric circles have the same center but different radii. A central angle is an angle having its vertex at the center of a circle.
DefinitionDefinitionDefinitionDefinition
(r,0)(r,0)
(1,0)(1,0)
x
y
ss
tt
From geometry it can be proved that the ratio of the arc length of two concentric circles is the same as the ratio of their radii:
From geometry it can be proved that the ratio of the arc length of two concentric circles is the same as the ratio of their radii:
11rr
ttss
==
Solving for s, s = rt , where s = arc length, r = radius, and t = angle measure (in radians).
Solving for s, s = rt , where s = arc length, r = radius, and t = angle measure (in radians).
In other words, the length of any arc equals the product of its radius and angle measure (in radians)
In other words, the length of any arc equals the product of its radius and angle measure (in radians)
Find the measure of the angle that cuts off an arc length of 8 in a circle with radius 2.
Find the measure of the angle that cuts off an arc length of 8 in a circle with radius 2.
s = rt8 = 2(t)t = 4 radians
s = rt8 = 2(t)t = 4 radians
EXAMPLE 2 Find the measure of the angle that cuts off an arc length of 7 in a circle of radius 4.
EXAMPLE 2 Find the measure of the angle that cuts off an arc length of 7 in a circle of radius 4.
Answer s = rt
7 = 4t
t = 7/4 = 1.75 radians
Answer s = rt
7 = 4t
t = 7/4 = 1.75 radians
Practice Question: Find the measure of the angle that cuts off an arc length of 8 in a circle of radius 5.
Practice Question: Find the measure of the angle that cuts off an arc length of 8 in a circle of radius 5.
Answer s = rt
8 = 5t
t = 8/5 = 1.6 radians
Answer s = rt
8 = 5t
t = 8/5 = 1.6 radians
Homework:
pp. 6-8
Homework:
pp. 6-8
►A. ExercisesSketch each angle in standard position.
3. 2/3
►A. ExercisesSketch each angle in standard position.
3. 2/3
00
22
32
32
Sketch each angle in standard position.
290°
Sketch each angle in standard position.
290°
00180°180°
270°270°
►A. ExercisesComplete each line of the following table.►A. ExercisesComplete each line of the following table.
Radians Degrees
9. 15
11.
15.
17. 31
6
7
7
12
/12/12
210210
309309
0.540.54
►B. ExercisesGive three angle measures in radians which are coterminal with each of the following. Include at least one positive and one negative angle measure.
21.
►B. ExercisesGive three angle measures in radians which are coterminal with each of the following. Include at least one positive and one negative angle measure.
21.44
►B. Exercises23. How many radians are in one degree?►B. Exercises23. How many radians are in one degree?
n rad (180) = degn rad (180) = deg
1 deg1 degn radn rad
180180
==
n =n =180180
0.01745 0.01745
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
Arc Length Radius Length Angle Measure(s) (r) (t)
8
5
4
2
6
32
25.
27.
29.
25.
27.
29.
Find the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
25. Given r = 8 and t = /4, use s = rt to
find the arc length (s).
Find the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
25. Given r = 8 and t = /4, use s = rt to
find the arc length (s).s = rt
= 8(/4)
= 2
s = rt= 8(/4)
= 2
Arc Length Radius Length Angle Measure(s) (r) (t)
8
5
4
2
6
32
22
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
25.
27.
29.
25.
27.
29.
Find the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
27. Given s = /2 and t = /6, use s = rt to
find the radius length (r).
Find the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
27. Given s = /2 and t = /6, use s = rt to
find the radius length (r).s = rt
/2 = r(/6)
r = 6/(/2) = 3
s = rt/2 = r(/6)
r = 6/(/2) = 3
Arc Length Radius Length Angle Measure(s) (r) (t)
8
5
4
2
6
32
22
33
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
►B. ExercisesFind the missing angle measures, radius measures, and arc lengths in the table below. Give the angle measures in radians.
25.
27.
29.
25.
27.
29.
►B. ExercisesDetermine the distance between each pair of points and also the midpoint of the segment joining them.
30. (3, -6), (1, 0)
►B. ExercisesDetermine the distance between each pair of points and also the midpoint of the segment joining them.
30. (3, -6), (1, 0)
d = (x2 – x1)2 + (y2 – y1)2d = (x2 – x1)2 + (y2 – y1)2
midpoint = ( , )midpoint = ( , )x1 + x2
2x1 + x2
2y1 + y2
2y1 + y2
2
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
(9, -2) =(9, -2) =22
5 + y5 + y,,
223 + x3 + x
18 = 3 + x18 = 3 + x22
3 + x3 + x9 =9 =
x = 15x = 15
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
-4 = 5 + y-4 = 5 + y22
5 + y5 + y-2 =-2 =
y = -9y = -9
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
B = (15, -9)B = (15, -9)
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
►B. ExercisesIf M is the midpoint of AB, find B. Then use distances to justify your answers.
35. A(3, 5), M(9, -2)
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