Question
Question: If the circles x<sup>2</sup> + y<sup>2</sup> + 2x + 2ky + 6 = 0 and x<sup>2</sup> + y<sup>2</sup> + ...
If the circles x2 + y2 + 2x + 2ky + 6 = 0 and x2 + y2 + 2ky + k = 0 intersect orthogonally. then k is
A
2 or – 3/2
B
–2 or – 3/2
C
2 or 3/2
D
– 2 or 3/2
Answer
2 or – 3/2
Explanation
Solution
Use 2g1g2 + 2f1f2 = c1 + c2
{If two circle cuts orthogonally}
= 2 × 1 × 0 + 2. k × k = 6 + k
̃ 2k2 – k – 6 = 0
̃ 2k2 – 4k + 3k – 6 = 0
̃ 2k(k – 2) + 3(k – 2) = 0
̃ (2k+ 3)(k – 2) = 0
̃ k = – 3/2, 2