Question
Question: The circle x<sup>2</sup> + y<sup>2</sup> + 2lx = 0, lĪ R touches the parabola y<sup>2</sup> = 4x ex...
The circle x2 + y2 + 2lx = 0, lĪ R touches the parabola
y2 = 4x externally, then –
A
l> 0
B
l< 0
C
l> 1
D
None of these
Answer
l> 0
Explanation
Solution
Given equations x2 + y2 + 2lx = 0,
y2 = 4x centre of circle is (–l, 0) and radius is
λ2+0= l.
Clearly the circle will touch the parabola exterenally if centre of circle lies on –ve x axis i.e. l > 0.