Question 319932
What is the circumference of a circle if the area is {{{81pi}}}?
<pre><b>
Use the Area formula {{{A=pi*r^2}}} to find the radius; then use that
value for r in the circumference formula {{{C=2pi*r}}}. 

{{{A = pi*r^2}}}
{{{81pi=pi*r^2}}}
{{{(81pi)/pi=pi*r^2/pi}}}

{{{(81cross(pi))/cross(pi)=cross(pi)*r^2/cross(pi)}}}

{{{81=r^2}}}
{{{sqrt(81)=sqrt(r^2)}}}
{{{9=r}}}

{{{C = 2pi*r}}}
{{{C = 2pi*9}}}
{{{C=18pi}}}

Edwin</pre>