How to Find the Radius of a Semi Circle
Mathematically, a radius is a line that extends from the center of a circle to any point on that circle's outer edge. Therefore, finding the radius of a semicircle is just like finding the radius of a complete circle. The method for doing this is determined by what information is available in advance. Finding the radius of a semicircle can be accomplished if the circumference, diameter or area of the circle that the semicircle is part of is known.
Other People Are Reading
Things You'll Need
- Calculator
- Math formula: r = D/2
- Math formula: r = square root of A/π
- Math formula: r = C/2π
Instructions
-
Using Circumference
-
1
Use the circumference to determine the radius. The formula is: r = C/2π, where r is radius, C is circumference, and π or Pi is approximately 3.142.
-
2
Multiply 2 x 3.142. The product is 6.284.
-
-
3
Divide the circumference of the circle by the product in Step 2. For example, if the circumference is 6 inches, the formula would be: 6/6.284. The answer is approximately .9548. So, rounded to nearest hundredth, the radius of a semicircle with a circumference of 6 inches is .95 inch..
Using Diameter
-
4
Use the diameter to determine the radius. The formula is: r = D/2, where r is radius and D is diameter.
-
5
Divide the diameter by 2. For example, if the diameter is 7 inches, the formula becomes 7/2.
-
6
Do the division, 7 divided by 2, to determine that the answer, the radius, is 3.5 inches.
Using Area
-
7
Use the area of a circle that a semicircle would be part of to determine the radius. The formula is: r = square root of A/π, where r is radius, A is area, and π or Pi is approximately 3.142.
-
8
Divide the area of the circle by Pi. For example, if the area of the circle is 10, divide 10 by 3.142. The answer is approximately 3.182.
-
9
Calculate the square root of the answer from step 2, which is 3.182. The answer, or radius, is approximately 1.784.
-
1
References
- Photo Credit sot/Stockbyte/Getty Images
