Here we will answer the following three questions. a) What is 9Pi? (What is 9π?), b) What is the area of a circle if the radius is 9?, and c) What is the circumference of circle if the radius is 9?
9π is another way of writing 9 times Pi (9 x 3.14). Therefore, the answer to our first question is:
9π = 28.27
Area: Next, we will calculate the area of a circle if the radius is 9. The formula for the area of a circle is πr2, which means that the area of a circle with a radius of 9 is:
π92 = 254.47
Circumference: Finally, we will calculate the circumference of a circle if the radius is 9. The formula for the circumference of a circle is 2πr, which means that the circumference of a circle with a radius of 9 is:
2π9 = 56.55
Note: π or Pi has an infinite number of decimals. For our calculations on this page with a radius of 9, we used Pi with eleven decimals as 3.14159265358 and then we rounded all our answers to two decimals.
Helpful Definitions:
Radius: The distance between the center of a circle to the edge of the circle. In our example on this page it was 9.
Diameter: The distance between one side of a circle to the exact opposite side of the circle. This is the same as 2 times radius. (For example, if the radius is 9, then the diameter must be 18.)
Pi: The ratio of a circle's circumference to its diameter. This is a fixed number regardless of circle size.
We used the following formulas on this page, where A is Area of circle, C is Circumference of circle, and r is radius:
A = πr2
C = 2πr
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