Grade Eight Math Problems for Finding the Area of a Circle
The area of a circle equals the number of square units inside the circle. The area can be found using geometry if the circle's diameter or radius is known. The diameter is the distance across the circle. The radius of a circle is the distance from its center to the edge or half of the diameter.
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Find the Circle's Area With the Radius
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The easiest way to find the area of a circle is to calculate using its radius. The formula for this is A = Pi • r^2 or A = Pi • r • r where Pi equals 3.14, r is the radius of the circle and A is the area. Therefore, if the radius of a circle is three inches, using the the formula express the problem as = 3.14 • (3 in) • (3 in) or = 3.14 • (3 in^2). Solving for A shows that this circle's area is 28.26 in^2.
Find the Circle's Area With the Diameter
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Divide the diameter of the circle by two to find the circle's radius. Next, use the formula or A = Pi • r^2 or A = Pi • r • r where Pi equals 3.14, r is the radius of the circle and A is the area. Therefore, if the diameter of a circle is eight inches, divide eight by two. Now the problem can be expressed as A = 3.14 • (4 in) • (4 in) or = 3.14 • (4 in^2). Solving for A shows this circle's area is 50.24 cm^2.
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Find the Radius or Diameter using the Area
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Use the same formula, A = Pi • r^2 or A = Pi • r • r where Pi equals 3.14, to begin calculating the radius or diameter of a circle. For example, if the area (A) of a circle is 78.5 meters, express the problem as 78.5m = 3.14 • r • r. Next, divide 78.5m by Pi, which is expressed as 78.5m/3.14 = r • r. Now the problem is 25m^2 = r • r. Therefore, the answer is r = 5m. The radius is 5m, and can be multiplied by two to find the diameter, which is 10m.
More Problems
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Find the area of a circle that has a radius of nine inches. The formula is A = 3.14 • 9in^2 or A = 3.14 • (9in • 9in). The answer is 254in^2 or 254 square inches.
Find the area of a circle that has a diameter of 44 feet. The formula is A = 3.14 • (44ft/2)^2 or A = 3.14 • ((44ft/2) • (44ft/2)). The answer is 1,520ft^2 or 1,520 square feet.
Find the area of a circle that has a radius of five inches. The formula is A = 3.14 • 5in^2 or A = 3.14 • (5in • 5in). The answer is 79in^2 or 79 square inches.
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References
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