Circumference and Area of Circles

Circumference and Area of Circles.

By Alina Sanchez Mederos

​You will need to show your work on a piece of paper.

I wanted the piece of paper TURNED IN with your name on it before you leave today.

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)

Multiple Choice

The distance from the center of the circle to any point on the circle is called the...

• radius

• diameter

• circumference

• area

Multiple Choice

The distance all the way across the circle, but through the center, is called the...

• radius

• diameter

• circumference

• area

Multiple Choice

What is the measurement around the outside of a circle called?

• Diameter

• Circumference

• Radius

• Center

Multiple Choice

Is the red line a radius or diameter of the circle?

• Radius

• Diameter

Multiple Choice

Is the red line a radius or diameter of the circle?

• Radius

• Diameter

Multiple Choice

What is twice as long as a radius

• Center

• Diameter

• Tanget

• Arc

Multiple Choice

If the diameter of a circle is 10 cm, the radius is 5 cm.

• TRUE

• FALSE

Multiple Choice

What is the diameter?

• 5 in

• 10 in

• 3.14 in

• 15.84 in

Multiple Choice

If the radius of a circle is 7 m, what is the diameter?

• 3.5 m

• 14 m

• 25 m

• 21.14 cm

Multiple Choice

If the diameter is 50 m, what is the radius?

• 100 m

• 30 m

• 25 m

• 200 m

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

Multiple Choice

What is this symbol called?

• pi

• sigma

• radius

• omega

Multiple Choice

What is the actual definition of this sign?

• It's the line going across the circle and going through the center

• It's the line going from the center to the edge of a circle

• It's the ratio of the circumference to the diameter of a circle.

• It's any line that goes through the circle but doesn't go through the middle.

Multiple Choice

What is the approximate numerical value of this sign?

• 3.11

• 3.14

• 4.13

• 6.28

Circumference

• There are two fomulas for finding circumference

• C = πd

• C = 2πr

• Circumference is a little more than 3 times the diameter

Multiple Choice

What is the formula for finding the circumference of a circle?

• C = r²

• C = rd

• A = π·r²

• C = π·d

Multiple Choice

Find the circumference of the circle.

• 38.47 cm

• 10.99 cm

• 43.96 cm

• 21.98 cm

Multiple Choice

What is the circumference of this circle?

• 3.14 cm 

• 37.7 cm

• 24 cm

• 68.4 cm

Multiple Choice

What is the circumference of a circle with a radius of 8 units in terms of pi?

(C = 2𝜋r)

• 8𝜋 units

• 16𝜋 units

• 32𝜋 units

• 4𝜋 units

Multiple Choice

Cynthia wants to buy a round photo frame for her brother. The radius of the photo frame is 9 cm. What is the photo frame’s circumference?

• 28.26 cm

• 56.52 cm

• 4.5 cm

• 18 cm

Multiple Choice

A roundabout is a one-way circular intersection in the road. About how many feet would a car travel if it drove once around the roundabout? (Think about which formula to use: Are they providing the radius or diameter?

• ~240 ft

• ~940 ft

• ~470 ft

• ~50 ft

Multiple Choice

The circumference of a circle is 25.12 cm. What is the diameter to the nearest centimeter?

• 4 cm

• 8 cm

• 25 cm

• 75 cm

Multiple Choice

If my circumference is 163.28ft, what is my radius?

• 52ft

• 26ft

• 3.14ft

• 163.28ft

Area

• the measure inside the circle

• always in square units

• A = π r²

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

Example 1: Find the area of a circle if the radius is 8 cm. Leave your answer in terms of pi. 

Example 2: Find the area of a circle if the diameter is 12 inches. Use 3.14 for pi. 

Multiple Choice

When finding area of a circle, you will need to know the numbers for $$\pi$$  and _______

• Diameter

• Radius

• Circumference

• :)

Multiple Choice

What is the formula for finding the area of a circle?

• A = π·d

• C = 2·π·r

• A = π·r²

• C = π·d

Multiple Choice

What does r represent in the formula:

A = π·r²

• circumference

• radius

• diameter

• squared

Multiple Choice

What does $$4^2=$$  ?

• $$4\times4$$  

• $$4-4$$  

• $$4\div4$$  

• $$4+4$$  

Multiple Choice

When finding area of a circle, if diameter is given, we need to find radius. We can find radius by ___________ diameter by 2.

• Adding

• Subtracting

• Multiplying

• Dividing

Multiple Choice

Find the area of the circle.

• 176.6 cm²

• 706.5 cm²

• 23.6 cm²

• 50.24 cm²

Multiple Choice

Find the area of the circle.

• 18.84 m²

• 113.04 m²

• 37.68 m²

• 452.16 m²

Multiple Choice

What is the area of this circle?

• 25π

• 10π

• π

• 5π

Multiple Choice

Shring's dining room table is round and has a radius of 4.5 feet. What is the tabletop's area?

• 63.585 ft²

• 68.345 ft²

• 64.585 ft²

• 61.345 ft²

Multiple Choice

Marisa purchases a pot for her father's garden. The diameter of the bottom of the pot is 18 cm. What is the area of the pot's bottom? (Round to the nearest whole number.)

• 28 cm²

• 57 cm²

• 254 cm²

• 1017 cm²

Multiple Choice

Mr. Smith wants to cover his circular pool. If the pool has a diameter of 13 feet how much fabric would he need to cover the pool? (round to the nearest whole number)

• 41 ft²

• 133 ft²

• 250 ft²

• 531 ft²