Circles

Vocabulary

100

A line that intersects a circle at exactly one place

Tangent

200

An arc with a measure less than 180 degrees

Minor Arc

300

A segment with endpoints on the circle

Chord

400

An angle with a vertex at the center and two sides that are radii

Central Angle

500

An arc with endpoints on the diameter

Semicircle

Formulas

100

πr²

Area

200

2πr

Circumference

300

πd

Circumference

400

2r

Diameter

500

(x-h)² + (y-k)²=r²

equation of a circle

Area and Circumference

100

Find the circumference of a circle with diameter=58m

182.21 m

200

Find the area of a circle with radius = 12 ft

452.39 ft²

300

Find the circumference of a circle with radius = 7mm

43.98mm

400

Find the area of a circle with diameter = 18cm

254.47in²

500

What is pi?

3.141592653...

Radius and Diameter

100

Find the diameter if a circle with radius = 4.5in

9 in

200

Find the radius of a circle with diameter = 34 yd

17 yd

300

Find the radius of a circle with area = 380.13in²

r = 11 in

400

Find the diameter of a circle with circumference = 65.97 m

d = 21 m

500

What does area measure?  What does circumference measure?

Inside of a circle, outside of a circle

Equation of a Circle

100

Center: (-7, 3)

Radius: 5

(x+7)²+(y-3)²=25

200

Center: (0, -4)

Radius: 8

x²+(y+4)²=64

300

Find the center and radius.

(x-1)²+(y-9)²=81

Center: (1, 9)

Radius: 9

400

Find the center and radius.

(x+5)²+y²=100

Center: (-5, 0)

Radius: 10

500

Find the equation of the circle with center (2, -6) and point on the circle (1, 10)

(x-2)²+(y+6)²=257