- The circle \(C\) has centre \(A\) and equation
$$x ^ { 2 } + y ^ { 2 } - 2 x + 6 y - 15 = 0 .$$
- Find the coordinates of \(A\) and the radius of \(C\).
- The point \(P\) has coordinates ( \(4 , - 7\) ) and lies on \(C\). Find the equation of the tangent to \(C\) at \(P\).