- Express \(\sqrt { 22.5 }\) in the form \(k \sqrt { 10 }\).
- A circle has the equation
$$x ^ { 2 } + y ^ { 2 } + 8 x - 4 y + k = 0$$
where \(k\) is a constant.
- Find the coordinates of the centre of the circle.
Given that the \(x\)-axis is a tangent to the circle,
- find the value of \(k\).