The area of circle c is 81 pi . if the radius of the circle is doubled, what is the circumference of the new circle ?
please answer and explain
162 pi
my answer is 162 pi too, but the answer is
a. 18 pi
b. 36 pi
c. 36 pi^2
d. 324 pi
e. 324 pi^2
if a = 81pi, r = 9
if r = 18, c = 36pi
To find the circumference of the new circle after doubling the radius, we need to use the formula for the circumference of a circle. The formula for the circumference of a circle is C = 2πr, where C is the circumference and r is the radius.
Given that the area of the circle c is 81π, we can find the radius using the formula for the area of a circle, which is A = πr^2. Rearranging the formula, we get r = √(A/π).
Substituting the given area, we have r = √(81π/π) = √81 = 9.
Now, if we double the radius to 9 x 2 = 18, we can calculate the new circumference using the formula C = 2πr.
C = 2π(18) = 36π units.
Therefore, the circumference of the new circle would be 36π units.