the area of a circle is represented by the following equation; A=pi*R2 where A is area, pi is the number pi (3.1415926.......for most high school maths, 3.14 is suitable) and R is the radius. So, square your radius, and multiply it by pi.
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Its just the area of a circle 21 inches or 21 centimeters? area of a circle is (pi)*r2 where pi = 3.1415.... and r = radius thus A = (3.1415)*(diameter/2)2 u can figure out the answer from that with a calculator
If radius=21 ft, then diameter = 2*radius = 42 ft
the radius is 10.5 inches. * * * * * Wrong! Circumference = 2*pi*Radius Or, Radius = Circumference/(2*pi) So circumference = 21 inches implies radius = 3.34 inches (to 3 sf)
Well, let's imagine that circle as a happy little friend on our canvas. To find the square footage, we first need to find the radius by dividing the diameter by 2. So, with a 42-inch diameter, the radius would be 21 inches. Then we can use the formula for the area of a circle, which is π times the radius squared. Just remember, there are about 0.00595 square feet in one square inch, so you can use that to convert your final answer.
Well, darling, the circumference of a circle is calculated using the formula C = 2πr. So, with a radius of 21 cm, you just plug that bad boy in and get C = 2 x π x 21 = 132 cm. Voilà, there you have it!