Chapter 9 Section 6: Circles March 11, 2009

Find Circumference A Circle is the set of all points that are the same distance from a given point. The given point is the CENTER of the circle. Circumference : the distance around the circle. Center

A Circle is the set of all points that are the same distance from a given point.

The given point is the CENTER of the circle.

Circumference : the distance around the circle.

Inside the Circle Radius : a line segment that starts on the circle and ends at the center point. Chord : segment whose end points are on the circle. Diameter : a chord that passes through the center of the circle

Radius : a line segment that starts on the circle and ends at the center point.

Chord : segment whose end points are on the circle.

Diameter : a chord that passes through the center of the circle

Pi or π Pi or π, pronounced “pie,” is the ratio of Circumference (or C) to Diameter (or d). C = πd C/d = π Pi is constant = 3.14159265358979323846… Pi as a fraction = 22/7 Because every circle is the same, the ratio is always the same, which is why pi is a constant.

Pi or π, pronounced “pie,” is the ratio of Circumference (or C) to Diameter (or d).

C = πd

C/d = π

Pi is constant = 3.14159265358979323846…

Pi as a fraction = 22/7

Because every circle is the same, the ratio is always the same, which is why pi is a constant.

Pi C = πd If the d, or diameter, equals 1, then what is the Circumference (or C)? C = π(1), C = π

C = πd

If the d, or diameter, equals 1, then what is the Circumference (or C)?

C = π(1), C = π

Find the circumference of the circle with a diameter of 6ft. C = πd  the formula C (approx.) = 3.14(6ft)  Substitute C = 18.84  Simplify! 6 Feet

C = πd  the formula

C (approx.) = 3.14(6ft)  Substitute

C = 18.84  Simplify!

Find the Circumference of Each Circle Diameter = 200 miles Radius = 30 millimeters Diameter = 2.8 inches. About 628 Miles About 188.4 mm About 8.8 inches

Diameter = 200 miles

Radius = 30 millimeters

Diameter = 2.8 inches.

Making Circle (Pie) Graphs A CENTRAL ANGLE is an angle whose vertex is the center of a circle. There are 360 ° in a circle. To make a Pie Graph, find the measure of each central angle by finding the proportion.

A CENTRAL ANGLE is an angle whose vertex is the center of a circle.

There are 360 ° in a circle.

To make a Pie Graph, find the measure of each central angle by finding the proportion.

Use proportions to find the measures of the central angles. Juan’s Weekly Budget : Lunch (l) = 25% Recreation (r) = 20% Clothes (c) = 15% Savings (s) = 40% Find the percentage of 360 ° to find the degree measurement of the central angles. L = 90 ° R = 72 ° C = 54 ° S = 144 °

Juan’s Weekly Budget :

Lunch (l) = 25%

Recreation (r) = 20%

Clothes (c) = 15%

Savings (s) = 40%

AT HOME Use a cup opening or cap to make your circles if you don’t have a compass.

Use a cup opening or cap to make your circles if you don’t have a compass.

Blood Types of Population Tell me the degree measurements of the central angles if you were to make a Pie graph with this information. 43% 5% 12% 40% Type O Type AB Type B Type A 155 ° 18 ° 43 ° 144 °

Tell me the degree measurements of the central angles if you were to make a Pie graph with this information.

Students at Western High School: Find Central Angles. Students at Western High School work in the following places; restaurants, 140; library, 15; auto shop, 60; retail stores, 75; and other places, 30. Round the measures of the central angles to the nearest degree. Restaurant: 158 ° Retail: 84 ° Auto Shop: 68 ° Other: 34 ° Library: 17 °

Students at Western High School work in the following places; restaurants, 140; library, 15; auto shop, 60; retail stores, 75; and other places, 30. Round the measures of the central angles to the nearest degree.

Assignment #16: Pages 472-473: 1-24. Skip #20. Remember, if you need a circle and have no compass, then use a cup from home and trace the outside.

Pages 472-473: 1-24. Skip #20.

Remember, if you need a circle and have no compass, then use a cup from home and trace the outside.