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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\sqrt { \lambda ^ { 2 } + 0 }= l.

Clearly the circle will touch the parabola exterenally if centre of circle lies on –ve x axis i.e. l > 0.