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C = 131.95 inches.

Q: How many inches is the circumference of a circle if its radius is 21 inches?

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It is: circumference/radius = 2*pi

The circumference of an 8 inch circle is: 25.13 inches(diameter x Pi = circumference).

Circumference = 2*pi*radius or pi*diameter Circumference = 36pi inches

Area of a circle: pi*radius*radius

Circumference of a circle: 2*pi*radius or diameter*pi Area of a circle: pi*radius squared

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you have to quote the diameter or radius or circumference of the circle to calculate the area. If diameter 78.53. If radius 314.15. If circumference 7.95

The circumference is about 131.9 inches. (C = r x 2 x Pi)

you have to quote the diameter or radius or circumference of the circle to calculate the area. If diameter 78.53. If radius 314.15. If circumference 7.95

It is: circumference/radius = 2*pi

All depends what you mean by 18 inches, is that the circumference, the diameter or the radius

The circumference of an 8 inch circle is: 25.13 inches(diameter x Pi = circumference).

Circumference = 2*pi*radius or pi*diameter Circumference = 36pi inches

The circumference of a circle, with a diameter of 12 inches, is 37.7 inches.

Area of a circle: pi*radius*radius

Yes, providing that they stem from the center of the circle to its circumference.

Circumference of a circle: 2*pi*radius or diameter*pi Area of a circle: pi*radius squared

A circle that is 4.25 inches implies that its circumference is 4.25 inches; that is, it is 4.25 inches around. The formula for the circumference of a circle is given as c = 2Ï€r, where c is the circumference, pi is a constant (approximately 3.14), and r is the radius of the circle. Since the c-value is known we can use algebra to manipulate the formula in order to solve for r (the only missing piece of information). Doing so yields r = c/2Ï€. Substituting the circumference of 4.25 inches into the formula reveals that the radius must be .68 inches (rounded to two decimal places). Now that the radius of the circle is known, the surface area can be calculated with the formula A = Ï€r2. Substituting the determined value of the radius in for r produces a surface area of 1.45 inches2. The unit of square inches comes from the fact that we are not only multiplying the numerical value of the radius, but also its units. In this case, r2 = (0.68 inches)(0.68 inches) = 1.45 inches2.