9 The points \(A\) and \(B\) have coordinates \(( 4 , - 2 )\) and \(( 10,6 )\) respectively. \(C\) is the mid-point of \(A B\). Find
- the coordinates of \(C\),
- the length of \(A C\),
- the equation of the circle that has \(A B\) as a diameter,
- the equation of the tangent to the circle in part (iii) at the point \(A\), giving your answer in the form \(a x + b y = c\).