Equation Of A Circle

A circle with centre (m,n) and radius r, has equation

(x-m)² + (x-n) ² =r²

A circle C has equation x² + y² -6x+2y -15=0

The coordinate of the centre and the radius are:

(x-3)² -9 + (y+1)^{2 _} 1-15=

(x-3)² + (y+1)^{2 _} 25=(x-3)² + (y+1)² =25=5^{2 5} Circle centre (3, -1) and radius 5