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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