Page 253 - ABCTE Study Guide_Neat

Previously, we reviewed formulas to measure triangles and quadrilaterals.

About Circles

A circle is the set of all points in a plane that are equidistant from a given point, called the center.

A radius of a circle is a segment that joins the center of the circle to any point on the circle.

A diameter of a circle is a segment that contains the center of the circle and whose endpoints lie on the
circle.

Circumference

Recall that the perimeter of a figure is the distance around the figure. Well, circumference is just the
perimeter of a circle. Like perimeter, the units of circumference are one-dimensional, like inches or
centimeters.

The circumference of a circle is given by the formula , where is the irrational number pi and r is
the radius.

Since the diameter of a circle is twice the radius ( ), the formula is an equivalent formula. You
may choose which formula to use based on the information that you’re given.

Question

What is the circumference of a circle of radius 8 m? Round your answer to the nearest meter.

A 19 m

B 25 m

C 50 m

D 101 m

Answer

Choice C is the correct answer. Since the radius of the circle is given, use the formula ,
where r = 8 m.