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It is not clear whether the circumference is 9 feet and you want the radius or diameter, or you have either the radius or diameter - which is 9 ft - and you want the circumference.
The formulas are
Circumference = 2*pi*r = 2*pi*d
where r is the radius, d the diameter, and pi is the mathematical constant approximated by 3.14159
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Which equation can be used to find the circumference of a circle with a radius that measures 10 feet?
Circumference = 2*Ï€*radius = 20*Ï€ feet
What is the circumference of a circle 2 m radius?
By using the equation 2πr that is used to find the circumference, you get 12.56m
Which equation could be used to find the circumference of a ball with a radius of 5 inches?
The circumference of a circle equals 2 times pi times the radius, in this case, about 31.42 inches.
What is the reason for pi?
In Geometry, pi lets us determine a circle's circumference if we know the circle's diameter (or radius, which is half the circle's diameter). We can determine this because the circumference is always pi (~3.14) times larger than the diameter of the circle. So, if the diameter of a circle is 1 foot, we know the circumference is 1 ft x pi which is approximately 3.14 feet. The formula for circumference is C = 2 x pi x r. Multiplying the 2 and the r (radius) in that equation gives you the length of the diameter of the circle, so the equation can be rewritten as C = pi x d which is what I used in the example in the last paragraph. Pi is also used to find the area of a circle by using the equation A=pi x r2. Calculus was used to create that formula which is beyond the scope of this explanation.
What formula is used to find the circumference when you know the radius?
Circumference=2*pi*radius
