The Cookie Monster encounters a cookie whose boundary is the equation $x^2+y^2 - 6 = 6x + 2 y$ and is very confused. He wants to know if this cookie is a lunch-sized cookie or a snack-sized cookie. What is the radius of this cookie?
Completing the square, you get that the radius is 8.
it's actually 4
\(x^2+y^2 - 6 = 6x + 2 y\\ (x^2-6x)+(y^2-2y)=6\\ (x^2-6x+9)+(y^2-2y+1)=6+10\\ (x-3)^2+(y-1)^2=4^2 \)
the radius is 4 units