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Area of a circle

# Radius & diameter from circumference

Sal finds the radius and diameter of a circle given the circumference.

## Want to join the conversation?

• I need help, How do u find the circumference with the given radius?
• The circumference given the radius can be found using C = 2πr
C is the circumference
• no it did not help what is 3.14
• 3.14 is π (pi, and infinite number) rounded to the nearest hundredth.
• um i really need help with this i keep getting confused with circumference and radius
• simple answer circumference is the distance around the circle
radius is the distance from the middle of the circle to any point on the circle hope it helps
• okay so if to find circumference= 2pir could it just be diameter x pi? To find circumference?
• Yes, both ways work. The only reason to use one or the other is if you are only given the number of the radius or if you are only given the number of the diameter.
• so the diameter x Pi = my answer? i feel a tad bit lost.
• welcome to the club, i had to have an senior explain it to me X3
(1 vote)
• If Radius is 3 = diameter 6

Circumference of the Circle-
Formula -2pir
2 x 3.14 x 2=

Diameter =2
3.14 x 2= C
• Except that you are only giving an approximation of the circumference. If R = 2, then C = 4π, and if D=2, C = 2π both are exact answers.
• Why is this so complicated? Why does pi go on forever?
• Pi is an irrational number, which means it cannot be represented as a simple fraction, and those numbers cannot be represented as terminating or repeating decimals. Therefore, the digits of pi go on forever in a seemingly random sequence..hope this helps!:D
• SO how do i find the radius by just knowing the circumference? Why did he divide 49 by 2 pi? where did 2 come from?
• If you start from the circumference formula, C=2πr, to isolate the r, you have to divide by 2π, thus r= C/(2π).
• So circumference and diameter are always the same numbers?
• The circumference is the diameter times pi (𝝅).
Example:
If the diameter is 12 then the circumference is 12𝝅

𝝅 is generally difficult to calculate, since it goes on forever you can write it in terms of 𝝅 (12𝝅).

You could also times the diameter by 3.14 to estimate it.
Example:
If the diameter is 12 then the circumference is 37.68.

Hope This Helps!