- The point \(A\) has coordinates ( 4,6 ).
Given that \(O A\), where \(O\) is the origin, is a diameter of circle \(C\),
- find an equation for \(C\).
Circle \(C\) crosses the \(x\)-axis at \(O\) and at the point \(B\).
- Find the coordinates of \(B\).
- Find an equation for the tangent to \(C\) at \(B\), giving your answer in the form \(a x + b y = c\), where \(a , b\) and \(c\) are integers.