How Do You Find The Radius Of A Circle If You Only Know Its Area

Maybe your like

HOME

Math Central

Quandaries & Queries

Question from s, a parent:

how do you find the radius of a circle if you only know the area of the circle. Do you somehow reverse the Pi formula.

Thank you

Yes, you have the correct idea. The area A of a circle is given by

A = π r2

where r is the radius of the circle and π is approximately 3.1416. Dividing both sides of this equation by π gives

A/π = r2

and hence if you know A, divide it by π and then take the square root to find r.

I hope this helps, Penny

Math Central is supported by the University of Regina and The Pacific Institute for the Mathematical Sciences.