A circle \(S\equiv x^2+y^2+4x+2fy+c=0\) passes through the centre of the circle \(x^2+y^2-4x+6y-2=0\). If the line \(3x-3y=c\) passes through the centre of the circle \(S=0\), then the length of tangent from \((1,1)\) to the circle \(S=0\) is
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Length of tangent from point \(P\) to circle is \(\sqrt{S_1}\).