Q.

If the line x1=0  is the directrix of the parabola  y2kx+8=0,k0 and the parabola intersects the circle x2+y2=4  in two real distinct points, then the value of  |k| is

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answer is 8.

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Detailed Solution

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The equation of the parabola can be written as  y2=k(x8k)
Equation of the directrix is  x=ha
1=8kk4     (x=1)k2+4k32=0k=8or4
For k=4 , the parabola is y2=4(x2) whose vertex is (2,0) and touches the circle x2+y2=4 at the vertex
For k=8 , the parabola is y2=8(x+1). Which intersects the circle x2+y2=4 at two real distinct points as the vertex (-1,0) of the parabola lies inside the circle.
 

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