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Unit 6 – Introduction to Trigonometry
Degrees and Radians (Unit 6.2)
William (Bill) Finch
Mathematics DepartmentDenton High School
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Lesson Goals
When you have completed this lesson you will:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
W. Finch DHS Math Dept
Radian/Degree 2 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Angles in Standard Position
An angle in standard position:
I starts on positive x-axis(initial side)
I rotates counter-clockwise forpositive angles
I rotates clockwise for negativeangles
I often named with Greek lettersI theta . . . θI alpha . . .αI beta . . .β
x
y
Initial
Terminal
Positive
x
y
Initial
Terminal
Negative
W. Finch DHS Math Dept
Radian/Degree 3 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Degree Measure
x (0◦)
y
0◦
30◦
60◦90◦
120◦
150◦
180◦
210◦
240◦
270◦300◦
330◦
360◦
45◦135◦
225◦ 315◦
W. Finch DHS Math Dept
Radian/Degree 4 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Degree-Minutes-Seconds (DMS)
A fraction of a degree can be expressed as a decimal fraction,but historically the degree was divided into minutes (′) andseconds (′′).
1◦ = 60′ and 1′ = 60′′
For example, 32.125◦ = 32◦ 7′ 30′′
Read “ 32 degrees, 7 minutes, and 30 seconds.”
W. Finch DHS Math Dept
Radian/Degree 5 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Degree-Minutes-Seconds (DMS)
A fraction of a degree can be expressed as a decimal fraction,but historically the degree was divided into minutes (′) andseconds (′′).
1◦ = 60′ and 1′ = 60′′
For example, 32.125◦ = 32◦ 7′ 30′′
Read “ 32 degrees, 7 minutes, and 30 seconds.”
W. Finch DHS Math Dept
Radian/Degree 5 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 1
Convert to decimal degrees.
a) 25◦ 15′
b) 12◦ 10′ 33′′
W. Finch DHS Math Dept
Radian/Degree 6 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Calculator Instructions – TI-84
W. Finch DHS Math Dept
Radian/Degree 7 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 2
Convert to degree-minutes-seconds.
a) 48.4◦
b) 21.456◦
W. Finch DHS Math Dept
Radian/Degree 8 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Calculator Instructions – TI-84
W. Finch DHS Math Dept
Radian/Degree 9 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
One radian is the measure of acentral angle θ that intercepts anarc s equal in length to the radius rof the circle:
θ =s
r
where θ is measured in radians.
x
y
r
srθ
Note that in the diagram above the radius r of the circle is thesame length as the arc s intercepted by the two radii, soθ = 1 rad when s = r .
W. Finch DHS Math Dept
Radian/Degree 10 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
The circumference of a circle isone revolution around the circle.
C = 2πr
s = 2πr
s
r= 2π
θ = 2π
θ ≈ 6.28
x
y
θ
A central angle θ that is one revolution is 2π radians.
W. Finch DHS Math Dept
Radian/Degree 11 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
One revolution around a circle is slightly more than 6 radians.
x
y
r1 rad2 rad
3 rad
4 rad 5 rad
6 rad
s = r
W. Finch DHS Math Dept
Radian/Degree 12 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
x
y
0◦
30◦
60◦90◦
120◦
150◦
180◦
210◦
240◦
270◦300◦
330◦
360◦
45◦135◦
225◦ 315◦
π6
π4
π3
π22π
33π4
5π6
π
7π6
5π4 4π
3 3π2
5π3
7π4
11π6
2π
W. Finch DHS Math Dept
Radian/Degree 13 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Special Angles – Learn Them!
x
y
π
x
y
2π
x
yπ2
x
y
3π2
W. Finch DHS Math Dept
Radian/Degree 14 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Special Angles – Learn Them!
x
yπ4
x
y
5π4
x
y3π4
x
y
7π4
W. Finch DHS Math Dept
Radian/Degree 15 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Special Angles – Learn Them!
x
yπ3
x
y
4π3
x
y2π3
x
y
5π3
W. Finch DHS Math Dept
Radian/Degree 16 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Special Angles – Learn Them!
x
y
π6
x
y
7π6
x
y
5π6
x
y
11π6
W. Finch DHS Math Dept
Radian/Degree 17 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian Measure
θ = π θ = 0
θ =3π
2
θ =π
2 Quadrant I
0 < θ <π
2
(acute angles)
Quadrant IIπ
2< θ < π
(obtuse angles)
Quadrant III
π < θ <3π
2
Quadrant IV3π
2< θ < 2π
W. Finch DHS Math Dept
Radian/Degree 18 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Radian-Degree Conversion
Set up and solve this proportion:
radian
degree=π rad
180◦
Hint – always set up the proportion with the unknown anglemeasure in the numerator.
W. Finch DHS Math Dept
Radian/Degree 19 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 3
Convert to radian measure.
a) 120◦
b) −30◦
W. Finch DHS Math Dept
Radian/Degree 20 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 4
Convert to degree measure.
a) −3π
4
b)3π
2
W. Finch DHS Math Dept
Radian/Degree 21 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Coterminal Angles
Coterminal angles have the same initial and terminal sides.
x
y
α
βx
y
α
β
To find a coterminal angle to some angle θ either add orsubtract a multiple of 2π (or 360◦):
θ ± n · 2π θ ± n · 360◦
W. Finch DHS Math Dept
Radian/Degree 22 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Coterminal Angles
Coterminal angles have the same initial and terminal sides.
x
y
α
βx
y
α
β
To find a coterminal angle to some angle θ either add orsubtract a multiple of 2π (or 360◦):
θ ± n · 2π θ ± n · 360◦
W. Finch DHS Math Dept
Radian/Degree 22 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 5
Sketch the angle given (in radians): θ =2π
3
Then find two coterminal angles: one positive and onenegative.
W. Finch DHS Math Dept
Radian/Degree 23 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 6
Sketch the angle given (in radians): α = −π4
Then find two coterminal angles: one positive and onenegative.
W. Finch DHS Math Dept
Radian/Degree 24 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 7
Sketch the angle given (in degrees): β = 25◦
Then find two coterminal angles: one positive and onenegative.
W. Finch DHS Math Dept
Radian/Degree 25 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 8
Sketch the angle given (in degrees): θ = −150◦
Then find two coterminal angles: one positive and onenegative.
W. Finch DHS Math Dept
Radian/Degree 26 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Arc Length
The relationship between a central angle and the length ofthe intercepted arc is
s = rθ
where θ is in radians.
r
s
θ
W. Finch DHS Math Dept
Radian/Degree 27 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 9
A circle has a radius of 5 inches. Find the length of the arcintercepted by a central angle of 120◦.
W. Finch DHS Math Dept
Radian/Degree 28 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 10
Winnipeg, Manitoba (Canada) is approximately due north ofDallas. Winnipeg is at a latitude of 49◦ 53′ 0′′N, and Dallas isat a latitude of 32◦ 47′ 39′′N.
Use the given information to find the distance betweenWinnipeg and Dallas (assume the Earth is a perfect spherewith a radius of 4000 miles).
W. Finch DHS Math Dept
Radian/Degree 29 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Area of a Sector
A sector of a circle is the region bounded by two radii andtheir intercepted arc.
r
θ
The area of a sector is A =1
2r 2θ (where θ is in radians).
W. Finch DHS Math Dept
Radian/Degree 30 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 11
A sector has a radius of 12 inches and a central angle of 100◦.Find the area of the sector.
W. Finch DHS Math Dept
Radian/Degree 31 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 12
Find the approximate area swept bythe wiper blade shown, if the totallength of the windshield wipermechanism is 26 inches.
W. Finch DHS Math Dept
Radian/Degree 32 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Linear and Angular Speed
An object moving along an arc has alinear speed given by
ν =arc length
time=
s
t
An object moving along an arc hasan angular speed given by
ω =central angle
time=θ
t
θr
s
W. Finch DHS Math Dept
Radian/Degree 33 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Linear and Angular Speed
An object moving along an arc has alinear speed given by
ν =arc length
time=
s
t
An object moving along an arc hasan angular speed given by
ω =central angle
time=θ
t
θr
s
W. Finch DHS Math Dept
Radian/Degree 33 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
Example 13
A bicycle wheel has a radius of 35 cm.A chalk mark is made on the tire andthen the tire is spun completing one fullrevolution in 0.8 seconds.
a) Determine the linear speed of thechalk mark.
b) Determine the angular speed.
W. Finch DHS Math Dept
Radian/Degree 34 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35
Introduction Angles – Degrees Angles – Radians Coterminal Applications Summary
What You Learned
You can now:
I Understand an angle as a measure of rotation.
I Understand radian and degree measures.
I Be able to convert between radian and degree measure.
I Be able to calculate arc length and sector area.
I Be able to find angular and linear speeds.
I Do problems Chap 4.2 #1, 5, 11-25 odd, 29, 31, 33, 35,39, 41, 43, 45, 51, 55, 57, 59
W. Finch DHS Math Dept
Radian/Degree 35 / 35