McGraw-Hill Education GRE 2019

Circles

A circle is a group of points that are all equidistant from a central point, known

as the center. Any line segment that connects the center to a point on the circle

is called the radius. Any circle has infinite radii, and all radii for a given circle

are equal.

Radius

A chord is any line that connects two points on a circle. The diameter of a circle is

any chord that passes through the center of the circle. The diameter is the longest

possible chord.

Chord

Diameter

Note that for any given circle, the diameter is twice the radius. Thus when you are

provided with the diameter of a circle, you can determine its radius and vice versa.

A diameter is one type of chord.

Circumference and Area

Let’s now look at calculations that involve the diameter and radius. The

circumference of a circle is the perimeter of the circle. Think of it in the following

way: If you flattened the circle to be a straight line, the length of that straight line

would be the circle’s circumference.

Circumference = 8

Length = 8

There is a constant relationship between circumference and diameter:

circumference

diameter = π

From this, you can derive the formula for circumference:

circumference = π × diameter (d)

408 PART 4 ■ MATH REVIEW

04-GRE-Test-2018_313-462.indd 408 12/05/17 12:05 pm