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Q: How do you find the radius of a circle if area is 81 pi?

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The area is 9 feet. You find the square root of 81 which is 9. I want circumference, not area.

Area(A)/ Area(B) = pi*rA2/pi*rB2 = rA2/rB2 = 16/81

Area= pi x radius squared. So radius (9) squared = 81, 81 x 3.14. See related link for more info.

Radius 10, area = 100 pi; radius 9, area = 81 pi

Area of a circle of radius r = Ï€r2Area of circle of radius 9 In = Ï€(9)2 = Ï€ x 81 , putting value of pi we get= 3.14159625 x 81 = 254.46 sq. In

Area: pi9^2 = 81pi or 254.469 square cm rounded

Area of a circle with radius r = pir2Area of the largest circle = Area of the smallest circle + Area of the shaded regionSince areas of the smallest circle and the shaded region are 9pi and 72pi, the Area, A, of the largest circle isA = 9pi + 72pi = 81pi, where r2 = 81.Thus, the radius of the largest circle is 9

To find area of a circle, the formula is πr2 where π is pi. Half of the diameter is the radius (r) so you divide 18 by 2 to get the radius (9). then, you square it (multiply it by itself) giving you 81. You then multiply this by pi to get the area. The exact answer is 81π, with a good approximation of: 254.46900494077325231547411404563973361997072134938357149897

i believe that it is 18 if the radius is 9 edit: wrong, area = pi*radius^2 so it's 3.1415926535*81=254.469

Area of a circle = pi R2 = 81 pi = 254.47 square ft (rounded)

The area of a circle is figured out using the formula Now, the circle we are given has a radius of 9cm. So, the area of the circle would be: Area = 3.14 x (9)2 = 3.14 x 81 = 254.34 cm2 The area of the circle in question is 254.34 cm2

The area of a circle is equal to πr2 where π (pi) is equal to approximately 3.142 and r represents the radius of the circle. Because the question gives you the diameter and not the radius you have to use the measurement of the diameter to calculate the radius. Remember that the radius is equal to half the diameter. So if the diameter is equal to 18 feet, then the radius of this particular circle is equal to 9 feet. Plugging this into our equation for area we get: area = π(92) area = 3.142(81) area = about 254.5 ft2 (don't forget that the answer is in squared feet not just feet)

pi*radius squared = 81 square units Divide both sides by pi and then square root both sides to find the value of the radius. radius = 5.077706252 or 5 units in length to one significant figure 2 times radius = diameter = 10 units in length

radius = sq rt of (81/pi) = 5.077706252 diameter = 2*077706252 = 10.1554125 inches

The question cannot be answered because it does not state clearly what the 81 refer to and what you are trying to find.

648pi. (pi = 3.14159...)Area of a circle = (pi) x (radius squared)= (pi)(9 squared) = (pi)81.Area of a cylinder = area of circle x height.= (pi)81 x 8= 648(pi)

Radius is 9 so area of complete circle (360o) is 81 x 3.14 ie 254.34. Angle of sector is therefore 360 x 169.56/254.34 which is 240o

A circle with a radius of 81 cm has a circumference of 508.94 cm

Area of circle: 81*pi square feet

The radius is 9 feet because pi*92 = 81*pi

Area of circle: 81*pi square units

In every circle . . .Area = (pi) x (radius)2Diameter = 2 x radiusCircumference = (pi) x diameterIn this circle, Area = (pi) R2 = 81R2 = 81/piR = sqrt( 81/pi )Diameter = 2 x sqrt( 81/pi )Circumference = (pi) x 2 x sqrt( 81/pi ) = 2 x sqrt( 81 pi ) = 18 sqrt(pi) = 31.9042 (rounded)

x² + y² = 81.

x2 + y2 = 81

x2 + y2 = 81