Diameter means a straight line segment that passes through the center of the circle and has its endpoints on the sides of the circle.
Example problem: You have a circle tub with a diameter of 8 feet, and you want to build a white fence that creates a 6-foot wide space around the tub. To find the circumference of the fence that has to be created, you should first find the diameter of the tub and the fence which will be 8 feet + 6 feet + 6 feet, which will account for the entire diameter of the tub, plus the space between the tub and fence. The diameter for your circular fence is 8 + 6 + 6, or 20 feet. Now plug it into the formula, plug π into your calculator for its numerical value, and solve for the circumference: C = πd C = π x 20 C = 62. 8 feet
A radius is any line segment that extends from the center of the circle and has its other endpoint on the edge of the circle. You might notice this is similar to the C = πd formula. That’s because the radius is half as long as the diameter, so the diameter can be thought of as 2r.
C = 2πr C = 2π x 5 C = 10π C = 31. 4 inches
