Answer
$8$
Work Step by Step
Step 1. From the given equation, we have $(x-5)^2+(y-12)^2=25$, thus we can identify the center of the circle as $(5,12)$ and radius $r=5$
Step 2. The distance from the origin to this center is $d=\sqrt {5^2+12^2}=13$
Step 3. The shortest distance from the origin to the circle is the on the line connecting the origin to the center of the circle, and can be found as $d_m=d-r=8$
