We know that the radius is half of the diameter, and also that a circle's diameter multiplied by pi is the circumference, so we multiply 12 by 2 to get 24, then we multiply this by pi, so we can either express this as 24π units, or we can assume pi to be 3.1415926 and multiply this by 24 to get 75.3982224 units.
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They would have to give you enough information to eventually get the diameter. If they gave you the area of a circle and asked for the circumference, you can determine the radius, and from the radius the diameter, and then the circumference. If they said "What is the circumference if the area of a circle is 36pi?" Area of a circle is pi*r2, which would give us a value for r = 6 Diameter is 2*r, or = 12. Circumference is d*pi, or 12pi
To find the circumference of a circle with an area of 144π sq in, we first need to find the radius of the circle. The formula for the area of a circle is A = πr^2, where A is the area and r is the radius. Given that the area is 144π sq in, we can solve for the radius: 144π = πr^2, r^2 = 144, r = 12 inches. The circumference of a circle is calculated using the formula C = 2πr, so for a circle with a radius of 12 inches, the circumference would be 24π inches.
circumference = 2 x π x radius ⇒ radius = circumference ÷ 2π area = π x radius2 = π x (circumference ÷ 2π)2 = circumference2 ÷ 4π = 122 ÷ 4π = 36/π ≈ 11.46 square units.
If the diameter of a circle is 12 inches the circumference is: 37.7 inches (diameter x pi = circumference).