Student Taught Lesson: Circumference
Step 1: Pi
Pi (or π) is the ratio of a circle's circumference to its diameter. Pi is a very long decimal, and it is usually rounded to 3.14.
Step 2: Diameter to Radius
The equation for circumference uses radius. Some circles, though, only show diameter, the length across the center of the circle. The way to find the radius of a circle is very easy. For example:
The diameter of this circle is 12 cm. R = D/2, so dividing 12 by 2 gets us the radius.The radius is half of the diameter, so the radius for this circle is 6 cm.
Step 3: Finding Circumference
The equation for circumference is 2πr. To find the circumference of the circle above, we have to use this equation.
C = 2πr π = 3.14
C = 2 x 3.14 x 6
C = 37.68 cm
The circumference of this circle is 37.68 cm.
1. r = 10
2. r = 7
3. r = 12