If $3 x-6 y+10=0$ and $12 y-6 x+16=0$ are two tangents to a circle, then the radius of the circle is

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Professor PC Thomas Classes · Answer

Lines are parallel: $3x-6y+10=0$ and $3x-6y-8=0$. Distance $2r = \frac{|10 - (-8)|}{\sqrt{3^2+(-6)^2}} = \frac{18}{\sqrt{45}}$. $r = \frac{3}{\sqrt{5}}$.