2. A circle \(C\) has equation
$$x ^ { 2 } + y ^ { 2 } + 4 x - 10 y - 21 = 0$$
Find
- the coordinates of the centre of \(C\),
- the exact value of the radius of \(C\).
The point \(P ( 5,4 )\) lies on \(C\).
- Find the equation of the tangent to \(C\) at \(P\), writing your answer in the form \(y = m x + c\), where \(m\) and \(c\) are constants to be found.