Question
Question: If circles x<sup>2</sup> + y<sup>2</sup> – 3x + ly – 5 = 0 and 4x<sup>2</sup> + 4y<sup>2</sup> – 12x...
If circles x2 + y2 – 3x + ly – 5 = 0 and 4x2 + 4y2 – 12x + y – 9 = 0 are concentric then l equals
A
41
B
−41
C
81
D
−81
Answer
41
Explanation
Solution
x2 + y2 – 3x + ly – 5 = 0 ̃ centre º (3/2, –l/2)
x2 + y2 – 3x + 41y – 49 = 0 ̃ centre º (23,−81)
\ l = 41