Question

Identify the radius and the center of a circle whose equation is (x-5)^2 + y^2 = 81

Answer 1

$\bf \textit{equation of a circle}\\\\ (x- h)^2+(y- k)^2= r^2 \qquad center~~(\stackrel{}{ h},\stackrel{}{ k})\qquad \qquad radius=\stackrel{}{ r}\\\\ -------------------------------\\\\ (x-5)^2+y^2=81\implies (x-\stackrel{h}{5})^2+(y-\stackrel{k}{0})^2=\stackrel{r}{9^2}~~ \begin{cases} center~(5,0)\\ radius=9 \end{cases}$