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.
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
