Question 113728
The area of a circle is {{{A=pi*r^2}}}, so if you are given the area and need to determine the radius, you simply solve this equation for r, thus:


{{{pi*r^2=A}}}
{{{r^2=A/pi}}} Divide both sides by {{{pi}}}
{{{r=sqrt(A/pi)}}} Take the square root of both sides


Remember that, in general, when you take the square root of something you have to consider both the positive and negative square roots:  {{{2^2=4}}} AND {{{(-2)^2=4}}}.  However, in this case you can exclude the negative square root because you are trying to find a length measurement, and a negative number for a length measurement is absurd.


The other thing to consider when presenting your answer is that the Area was given in {{{cm^2}}}.  Taking the square root of a quantity measured in {{{cm^2}}} means that your result will be in cm.


Hope this helps,
John