Geometry Study Guide

• A

• B

• C

• D

Answer explanation

A "radius" is the distance from the center of a circle to any point on its edge.

Use the circle. Identify the diameter(s) of circle O.

Answer explanation

The diameter of a circle is a straight line that passes through the center of a circle and touches both sides of the circle's edge.

Use the circle. Identify the chord(s) of circle O.

Answer explanation

In math, a "chord" is like a straight line that connects two points on the edge of a circle, kind of like a string stretched across a round pizza; the longest chord of a circle is called the diameter, which goes straight through the middle of the circle. 

Find the missing length for a circle. Given r = 18.5 cm, d = ?.

• 38 cm

• 37 cm

• 9.5 cm

• 6.3 cm

Answer explanation

A "radius" is the distance from the center of a circle to any point on its edge, while a "diameter" is the distance across the whole circle through the center, which means the diameter is always twice as long as the radius; like cutting a pizza in half, the radius is from the center to the crust, and the diameter goes all the way across the pizza through the middle!

Find the missing length for a circle. d = 50 in., r = ?

Answer explanation

Radius is half the diameter

What is the diameter of the circle?

• 6.9 cm

• 62.4 cm

• 41.6 cm

• 10.4 cm

Answer explanation

Diameter is double the radius

Find the circumference of the circle with the given radius or diameter. Round to the nearest unit.

• 79 in.

• 1,963 in.

• 157 in.

• 28 in.

Answer explanation

2 x 3.14 x r = C

Find the circumference of the circle with the given radius or diameter. Round to the nearest unit.

• 227 cm

• 20 cm

• 27 cm

• 53 cm

Find the radius of a circle with the circumference of 381 inches. Use 3.14 for π. Round to the nearest tenth.

Find the area of the circle to the nearest tenth.

• 73.8 cm²

• 147.7 cm²

• 1,734.9 cm²

• 6,939.8 cm²