. The condition that the line
The condition that the line lx + my + n = 0 be normal to the circle x2 + y2 + 2gx + 2fy + c = 0 is
(a) lm = gf (b) lg + nf = m
(c) lg + mf = n (d) none of these
(c) Centre º (-g, -f)
The normal to given circle passes through centre.