High School Math : How to find the length of a radius

Study concepts, example questions & explanations for High School Math

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Example Questions

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Example Question #62 : Radius

The circumference of a circle is 45 inches.  The circle's radius is ____ inches.

Possible Answers:

Correct answer:

Explanation:

When you know the circumference of a circle, you can determine its diameter by dividing the circumference by .  Then, when you have the diameter, you can determine the radius by dividing the diameter by 2.

Example Question #5 : How To Find The Length Of A Radius

A circle with center (8, 5) is tangent to the y-axis in the standard (x,y) coordinate plane. What is the radius of this circle? 

Possible Answers:

5

4

16

8

Correct answer:

8

Explanation:

For the circle to be tangent to the y-axis, it must have its outer edge on the axis. The center is 8 units from the edge.

Example Question #1 : Radius

A circle has an area of . What is the radius of the circle, in inches?

Possible Answers:

24.5 inches

14 inches

49 inches

7 inches

16 inches

Correct answer:

7 inches

Explanation:

We know that the formula for the area of a circle is πr2. Therefore, we must set 49π equal to this formula to solve for the radius of the circle.

49π = πr2

49 = r2

7 = r

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