Question

What’s the equation of the circle with center (9, –1) and radius r = 7?

Answer 1

$\bf \textit{equation of a circle}\\\\ (x- h)^2+(y- k)^2= r^2 \qquad center~~(\stackrel{9}{ h},\stackrel{-1}{ k})\qquad \qquad radius=\stackrel{7}{ r} \\\\\\\ [x-9]^2+[y-(-1)]^2=7^2\implies (x-9)^2+(y+1)^2=49$