Question

The circle below is centered at (-1, 1) and has a radius of 3. What is its
equation?

Answer 1

$\bf \textit{equation of a circle}\\\\ (x- h)^2+(y- k)^2= r^2 \qquad center~~(\stackrel{-1}{ h},\stackrel{1}{ k})\qquad \qquad radius=\stackrel{3}{ r}\\[2em] [x-(-1)]^2+[y-1]^2=3^2\implies (x+1)^2+(y-1)^2=9$