Question

The lines $3x+4y=9$ and $6x+8y+15=0$ are tangents to the same circle. The radius of the circle is :-

• A. $\frac{3}{10}$
• B. $\frac{33}{20}$
• C. $\frac{33}{10}$
• D. $\frac{33}{5}$

Answer 1

The correct option is B $\frac{33}{20}$

The lines $3x+4y=9$ and $6x+8y+15=0$ are tangent to the same circle.

As both tangents are parallel then
radius =$\frac{1}{2}\left|\frac{-9-\frac{15}{2}}{\sqrt{3^2+4^2}}\right|=\frac{1}{2}.\frac{33}{10}=\frac{33}{20}$