Question

Given the circles x² + y² – 4x – 5 = 0 and x² + y² + 6x – 2y + 6 = 0. Let P be a point (a, b) such that the tangents from P to both the circles are equal. Then –

• A. 2a + 10b + 11 = 0
• B. 2a – 10b + 11 = 0
• C. 10a – 2b + 11 = 0
• D. 10a + 2b + 11 = 0

Answer 1

Answer: (C)

10a – 2b + 11 = 0

Answer 2

Q Tangents drawn from P to the 2 circles are equal

Ž locus of P is the radical axis

\ equation of the radical axis is 10a – 2b + 11 = 0

(S₁ – S₂ = 0)

(where S₁ and S₂ are the equation of the circles given).