if the area of a circle is 36 pi square feet , find its circumference .
"the area is given by pi * r * r . hence pi * r * r = 81 pi r * r = 36 ; hence r = 36 feet the circumference is given by 2 * pi * r = 2 * pi * 6 = 128 pi feet correct answer c"
circumface(sqrt(36))