If (- 3, 2) lies on the circle x2 + y2 + 2gx + 2fy + c = 0 which is concentric with the circle x2 + y2 + 6x + 8y – 5 = 0, then c =
Given that the point (- 3,2) lies on the circle x2 + y2 + 2gx + 2fy + c = 0 which is concentric with x2 + y2 + 6x + 8y - 5 = 0.
We know that concentric circles will have same centre.
Let us assume the concentric circle be x2 + y2 + 6x + 8y + d = 0. ..... - (ii)
Substituting (- 3,2) in (ii)
⇒ (- 3)2 + 22 + 6(- 3) + 8(2) + d = 0
⇒ 9 + 4 - 18 + 16 + d = 0
⇒ d = - 11
Substituting value of c in (ii) we get
⇒ x2 + y2 + 6x + 8y - 11 = 0
Comparing with x2 + y2 + 2gx + 2fy + c = 0 we get c = - 11
∴ The correct option is (b).