Question

circumference of circle whose area is 81pier2

Answer 1

As we know that, area  A = π r²
circumference C = 2×π×r
dividing both, we get,
A/C= r/2
⇒C=2A/r
now, A/q.
⇒C=( 2 × 81 π r²)/r
      =162 π r units

Answer 2

area = πr² = 81π
r² = 81
r = 9
perimeter = 2πr = 2×π×9 = 18π