Because the point A is reflected on the circle C through the X axis, it is equivalent to the point B (-1,-1) of the light source at the point A, which is symmetrical with the X axis, and the distance from B to the center C is s= root {[5-(- 1)] square+[7-(-65438).

The radius of a circle is r=2, so the shortest distance is s-r= 10-2=8.