11 Two circles have equations
\(x ^ { 2 } + y ^ { 2 } - 4 x = 0 \quad\) and
\(x ^ { 2 } + y ^ { 2 } - 6 x - 12 y + 36 = 0\).
- Find the centre and radius of each circle and hence show that the \(y\)-axis is a tangent to both circles.
- Find the equation of the line through the centres of both circles.
- Determine the gradient of a line other than the \(y\)-axis which is a tangent to both circles.
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