On shifting the origin to a particular point, the equation x2+y2−4x−6y−12=0 transforms to X2+Y2=K. Then K=
(x,y)=(X−h,Y−k)
(X−h)2+(Y−k)2−4(X−h)−6(Y−k)−12=0
X2+Y2−2Xh−4X−2Yk−6Y+h2+k2+4h+6k−12=0
Comparing coefficients
2h=−4
⇒h=−2
2k=−6
k=−3
∴h2+k2+4h+6k−12=4+9−8−18−12
=−25
∴X2+Y2=K=25