Chapter 13 - Conic Sections - 13.1 Conic Sections: Parabolas and Circles - 13.1 Exercise Set - Page 854: 34

$x^2+y^2=121$

Using $(x-h)^2+(y-k)^2=r^2$ or the Center-Radius form of the equation of circles, the equation of the circle with center $( 0,0 )$ and radius, $r= 11 ,$ is \begin{array}{l}\require{cancel} (x-0)^2+(y-0)^2=11^2 \\\\ x^2+y^2=121 .\end{array}