Basic Geometry : How to find circumference

Study concepts, example questions & explanations for Basic Geometry

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Example Questions

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Example Question #111 : How To Find Circumference

The area of a circle is . What is the circumference? 

Possible Answers:

Correct answer:

Explanation:

The area of a circle is , so in this case the radius squared is 4. Since the square root of 4 is 2, the radius has length 2. To find the circumference, use the formula . In this case, 

Example Question #301 : Plane Geometry

Circle radius

The radius of the circle shown here is  units long. What is its circumference?

Possible Answers:

Correct answer:

Explanation:

The formula for the circumference  of a circle given its radius  is . For the circle given in the problem,  units, and so

.

Hence, the circumference of this circle is  units.

Example Question #301 : Plane Geometry

A circle has diameter 20.

True or false: The circumference is greater than 60.

Possible Answers:

False

True

Correct answer:

True

Explanation:

The circumference of a circle is its diameter multiplied by , so, since the diameter is 20, the circumference is . Also, 

,

so, multiplying both sides by 20 by the Multiplication Property of Inequality, 

and

.

The circumference is indeed greater than 60.

Example Question #111 : How To Find Circumference

Ashley has a square room in her apartment that measures 81 square feet. What is the circumference of the largest circular area rug that she can fit in the space?

Possible Answers:

Correct answer:

Explanation:

In order to solve this question, first calculate the length of each side of the room. 

The length of each side of the room is also equal to the length of the diameter of the largest circular rug that can fit in the room. Since , the circumference is simply

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