Circles

Nothing special. Just some reminders.
Equation of circle: (x–h)² + (y–k)² = r²
Center = (h, k)
Radius = r

Another form of equation of circle:  x² + y² + Dx + Ey + F =0
Center = (-D/2, -E/2)
Radius = √(D/2)² + (E/2)²–F
Remember the coefficients of  x²  and  y² must be 1 when you are
calculating the center and radius.