Angles and Fractional Parts of a Circle

Parts of a Circle

• Radius: line segment that goes from the center to the edge of the circle (HALF the DIAMETER)

• Diameter: line segment that goes from edge to edge on a circle (TWICE the RADIUS)

• Circumference: the distance around the outside of a circle (AKA perimeter)

Circumference

• There are two fomulas for finding circumference

• C = πd

• C = 2πr

• Circumference is a little more than 3 times the diameter

What is Pi?

• the ratio of the circumference to the diameter of a circle (π= c/d)

• a greek symbol (π)

• approximately 3.14

• used when solving area and circumference of circles

Area

• the measure inside the circle

• always in square units

• A = π r²

• https://www.youtube.com/watch?v=YokKp3pwVFc

Area of a Circle & Semicircle

Area of a Quarter-Circle

If I want to find the area of an part of a circle, how would I do it?

Area of a Sector

Example 1:

Example 2

Multiple Choice

Find the area of a sector with a radius of 9ft and an angle measure of  $$132\degree$$  

• $$10.27ft^2$$  

• $$93.31ft^2$$  

• $$29.7ft^2$$  

• $$85ft^2$$  

Fill in the Blanks

Find the area of the sector shown. Round to the nearest hundredth

Multiple Choice

What is the area of the shaded sector?

• $$6.56yd^2$$

• $$7.49yd^2$$

• $$8.72yd^2$$

Multiple Choice

What is the formula for finding the area of a sector. 

• $$\left(\frac{n}{360}\right)\pi r^2$$

• $$2\pi r$$

• $$\pi r^2$$