Question

The area of a circle is found by the equation upper a equals pi r squared . if the area a of a certain circle is 81 pi square​ inches, find its radius r.

Answer 1

we know that
area of the circle =pi*r²
where r is the radius
clear the radius r
A=pi*r²------> divide by pi----> r²=A/pi--------->square root----> r=√[A/pi]
for Area=81*pi in²
r=√[80*pi/pi]---------> r=√80--------> r=8.94 in

the answer is
the radius is 8.94 in