Question

The line $3x-4y+4=0$ and $6x-8y-7=0$ are tangent to the same circle . The radius of the circle is

Answer 1

The diameter of the circle is the perpendicular distance between the parallel limes $3x-4y+4=0$and $3x-4y-\frac{7}{2}=0$ and so it is equal to

$\frac{4}{\sqrt{(9+16)}}-\frac{-7/2}{\sqrt{(9+16)}}=\frac{3}{2}\therefore r=\frac{3}{4}$