Question:
The line $2 \mathrm{x}-\mathrm{y}+1=0$ is a tangent to the circle at the point $(2,5)$ and the centre of the circle lies on $x-2 y=4$. Then, the radius of the circle is:
Correct Option: 1
Solution:
$\left.\begin{array}{l}\left(\frac{\mathrm{h}-\frac{(\mathrm{h}-\mathrm{i})}{2}}{2-\mathrm{h}}\right)(2)--1 \\ \mathrm{~h}=8\end{array}\right)$
center $(8,2)$
Radius $\left.=\sqrt{(8-2)^{2}+(2-5)^{2}}=3 \sqrt{5}\right)$