Question

Identify the radius of the circle whose equation is (x - 2)2 + (y - 8)2 = 16.

Answer 1

The radius is 4.

That equation is in center-radius form. When that’s the case, the radius is the square root of the number in the right of the equals sign. Square root of 16 is 4.

Answer 2

$\bf \textit{equation of a circle}\\\\ (x- h)^2+(y- k)^2= r^2 \qquad center~~(\stackrel{}{ h},\stackrel{}{ k})\qquad \qquad radius=\stackrel{}{ r}\\\\ -------------------------------\\\\ (x-\stackrel{h}{2})^2+(y-\stackrel{k}{8})^2=16\implies (x-2)^2+(y-8)^2=\stackrel{r}{4^2}$