9 The line \(y = 2 x + 5\) intersects the circle with equation \(x ^ { 2 } + y ^ { 2 } = 20\) at \(A\) and \(B\).
- Find the coordinates of \(A\) and \(B\) in surd form and hence find the exact length of the chord \(A B\).
A straight line through the point \(( 10,0 )\) with gradient \(m\) is a tangent to the circle. - Find the two possible values of \(m\).