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Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
CHAPTER 4: Trigonometry and the Unit CircleSection 4.1: Angles and Angle Measure
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
(A) Standard Position
When drawing an angle θ on the xy plane in standard position, the following conditions must apply:· Vertex must be at __________________________
· The initial arm lies on ______________________________
Angles are often classified according to the quadrant in which their terminal sides lie.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
(B) Positive and Negative Rotation (Standard Position)
(C) Reference Angle the acute angle that is formed by the terminal arm of the angle and either the positive or negative xaxis.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex)Sketch in standard position the following angles and identify the type of angle, its reference angle.
A) 300° B) 200° C) 800° D) 500°
Note: • For angles larger than 360º or smaller than 360º we subtract or add multiples of −360º to determine where the angle is.
Section 4.1 Angles and Angle Measuressoln.notebook
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There are two units for measuring angles:» Degrees» Radians
What is a radian?
A radian is an angle measurement that gives the ratio:
Each full radian measure occurs when the arc length is the same as the length of the radius
Angle Measure
• An angle measurement• One degree is defined as of a full rotation.
What is a degree?
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
When dealing with circles let's start with a special one, the unit circle. » The unit circle has a radius of 1
If the radius is 1 what is the angle of in radians?
Common Radian Measure
Angle Degrees Angle Radian90180270360453060
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex) Convert the following to radian measure (exact and approximate).
A) 135° B) 58° C) 225°
D) 144° E) 214.5° F) 118°
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex)Sketch the following angles in standard position.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Coterminal Angles
• angles in standard position with the same terminal arm and can be measured in degrees or radians
• Coterminal angles can be found by adding or subtracting multiples of 360° or 2π
• In general, if θ is an angle in standard position then any angle of the form:
θ ± 2πn, where n ∈ N or θ ± 360°n, where n ∈ N
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex)Find an angle that is coterminal with each of the following angles. Sketch to check your answer.
A) 112° B) 700°
D) 3
B)
C)
A) 515
Find one negative and one positive angle that is a coterminal with each angle.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex) Determine the measures of all angles that are coterminal with 120° in the given domain.
A) 0° ≤ θ ≤ 720° B) 360° ≤ θ ≤ 0°
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex)Write an expression for all of the angles coterminal with each angle. Indicate whatyour variable represents.
A) 310° B)
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Arc Length, Radius and the Radian Measure of the Central Angle
2 types of arc length:> Minor Arc> Major Arc
Determine a formula relating the radius (r), central angle θ (measured in radians) and arc length of a circle (a). [Earlier in the notes, the arc length was denoted by the variable s]
Arc Length = θ x radiusa = θr
Know how to rearrange!!
Ex) Determine the measures of the arc length subtended by the angles and radii below:
A) central angle of with radius of 10 cm.
B) central angle of 2.6 rad with radius of 4.9cm.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex) Determine the measure of the radius of a circle in the following diagram.
Ex) An arc of 20 cm in length cuts a circle of radius 5.4 cm. Determine the measure of the central angle in radians and degrees.
Section 4.1 Angles and Angle Measuressoln.notebook
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December 15, 2016
Ex) Find the radius of a circle in which an arc of 3 km subtends a central angle of 20o.
Ex) During a family vacation, you go to dinner at the Seattle Space Needle. There is a rotating restaurant at the top of the needle that is circular and has a radius of 40 feet. It makes one rotation per hour. At 6:42 p.m., you take a seat at a window table. You finish dinner at 8:28 p.m. Through what angle did your position rotate during your stay? How many feet did your position revolve?
Do questions 12 and 13 page 176.