Aim: What are radians and how do they differ from degrees?

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# Aim: What are radians and how do they differ from degrees? - PowerPoint PPT Presentation

Aim: What are radians and how do they differ from degrees?. Do Now:. A kite is held by a taut string pegged to the ground. If the string is 40 feet long and makes a 33 0 angle with the ground, how high is the kite?. h. h. h. Angle of elevation. 40’. 40’. 33 0.

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Aim: What are radians and how do they differ from degrees?

Do Now:

A kite is held by a taut string pegged to the ground. If the string is 40 feet long and makes a 330 angle with the ground, how high is the kite?

h

h

h

Angle of elevation

40’

40’

330

A kite is held by a taut string pegged to the ground. If the string is 40 feet long and makes a 330 angle with the ground, how high is the kite?

Sin 330 =

.544639. . . =

40 feet

h 21.8 feet

The kite is approximately 22 feet off the ground.

Circle - Central Angles

B

900

A

O

1800

Central Angle – of a circle is an angle

whose vertex is the center of the circle.

The sum of all central angles of a circle is 3600.

Arc AB = r

If the length of arc AB

measures r, then the

measure of central angle

1

2

3

4

5

6

.28

Definition: A radian is the measure of the

central angle that intercepts an arc equal

in length to the radius of the circle.

B

r

A

r

O

r

2

2 units

2

2

1

2

1

2

2

If the measure of arc AB

is 1 unit, then the

measure of central angle

Arc AB = 1

B

1

A

1

O

length of intercepted arc

Finding the Measure of Central Angles in Radians

B

s

A

r

O

measure of angle  in radians =

s

• Arc AB defines
• a semi-circle
• with
• length s.
• is the central

angle whose measure

is 1800.

B

A

r

O

s = 1/2 C =

C = pD = p2r

1/2 (2πr) = πr

= 1800

length of intercepted arc s

Measure of Central Angles in Radians

measure of angle  in radians =

B

s

A

O

r

π π

B

r

A

r

O

or 57º18’ (to the nearest minute)

What is the complement of  = /12?

Supplementary, Complementary & Coterminal Angles

What is the supplement of  = 5/6?

Name, in terms of radians, a coterminal angle for  = 17/6

r = 4

substitute the

given values

Model Problem

In a circle, the length of a radius is 4

centimeters. Find the length of an arc

intercepted by a central angle whose

solve for s

s = 6 cm.

Model Problem

A weather satellite in a circular orbit around Earth completes one orbit every 3 hours. The radius of the Earth is about 6400 km, and the satellite is positioned 2600 km above Earth. How far does the satellite travel in 1 hour.

s

since one complete

rotation takes 3 hr.,

the satellite completes

1/3 of a rotation in 1hr.

r

s = distance traveled in 1 hr.

r = 6400 + 2600 = 9000

Proportion:

x = degrees

solve for x:

How do we convert a π/4 radians to degrees?

Method 1

πx = 45π

x = 45 degrees

Substitution:

How do we convert a π/4 radians to degrees?

Method 2

mA in degrees

measure of a straight angle in degrees

=

measure of a straight angle in radians

Proportion:

identify variable:

x = measure in

set up proportion

solve for x

Degrees to Radians – Model Problem

Use the fact: π radians = 1800

180x = 75π

Method 1

Proportion:

x = degrees in

solve for x:

Model Problem

πx = 420π

x = 420 degrees

Model Problem (con’t)

Method 2

Substitution:

Proportion:

identify variable:

x = measure in

set up proportion

solve for x

Model Problems

180x = 135π

Regents Prep

What is the number of degrees in an angle whose radian measure is

• 150 2. 165
• 3. 330 4. 518

Find to the nearest minute, the angle whose measure is 3.45 radians.

x = 197.6704o

x = 197o 40’

convert .6704o to minutes

m’ = 40.2’

Model Problem

In a circle, a central angle of 1/3 radian intercepts an arc of 3 centimeters. Find the length, in centimeters, of a radius of the circle.

If  is 4 and r = 1.25, find s.

Model Problem

If f(x) = cos 2x and sin x, find f(/2)

substitute

simplify

evaluate

If f(x) = sinx cos2x, find f(/3)