Question
Question: The parabola y<sup>2</sup> = 4ax and circle x<sup>2</sup> + y<sup>2</sup> + 2bx = 0 have more than o...
The parabola y2 = 4ax and circle x2 + y2 + 2bx = 0 have more than one common tangent if-
A
ab> 0
B
ab < 0
C
ab < –2
D
ab > 2
Answer
ab> 0
Explanation
Solution
For more than one common tangent the focus and centre (–b, 0) should lie on opposite side of origin as both pass through origin.
\ a (–b) < 0 ̃ ab > 0