The equation of the circle whose centre is (1, -3) and which touches the line 2x-y-4=0 is
x2 + y2 - 10x + 30y - 49 = 0
r = d = ∣∣∣2+3−4√4+1∣∣∣=1√5
(x−1)2+(y+3)2=15