All About Circles

Vocabulary

100

A line from the center of a circle to the circle

Radius

200

The outline of a circle

Circumference

300

A line from one point of the circle, through the center and then to another point of the circle

Diameter

400

the whole inside space of the circle

Area

500

A line segment joining any two points on the circumference of the circle

Chord

Formulas

100

Formulas for diameter

2πr or πd

200

Formula for area

πr²

300

Formula for radius from area

(A/π) square rooted

400

Area = 21.26m²

r = ?  (round to nearest hundredths place)

r = 2.6m

500

r = 150mm

C = ? (round to the hundredths place)

C = 942mm

Questions

100

r = 999cm

A = ? (round to the hundredths place)

A = 3133723.1cm squared

200

The diameter of a circle is 3.14m long. What is the circumference of the circle? (round to the nearest hundredth)

C = 9.86m

300

Nate wants a new basketball rim. Nate wants the basketball rim to have an area of 142cm. What is the diameter of the basketball rim? (round to the nearest hundredth)

d = 13.45cm

400

Greg plays hockey and decides to make a new puck. The new puck has a area of 457mm squared. What is the diameter of Greg's puck? (round to the nearest hundredths)

C = 75.76mm

500

A circle has an area of 9000m. What is the circumference of the circle? (round to the nearest hundredth)

C = 336.21m

Radius

100

d = 10

r = ? (round to the nearest hundredth) 

r = 5

200

d = 12349m

r = ? (round to the nearest hundredth)

r = 6174.5m

300

C = 999πcm

r = ? (round to the nearest hundredth)

r = 499.5cm

400

Hasan finds the circumference of a pizza which is 21cm. What is the radius of the pizza? (round to the nearest hundredth)

r = 3.34cm

500

Ms. D corrects a student's worksheet. The worksheet has a problem with a circle which has an area of 1400πmm. What is the radius of the circle? (round to the nearest hundredth)

r = 37.42mm

Mystery Questions

100

π is used as ?

3.14

200

What is the formula for circumference from area?

C = 2(square root(πA)

300

If there is a question with the area of any number x π, what is an easy way to find area without any extra step?

Ex: A = 566πm   r = ? (round to the nearest hundredth)

You can remove pi from the equation to find radius: (566π/π)square root)  = 566 square root, and then just square root that number: (566 square root).

Ex: r = 23.79m

400

What formulas uses square root?

Radius from area and circumference from area.

500

What is π?

π is the ratio of a circle's circumference to a circle's diameter.