Let A and B be two distinct points on the parabola y2=4x. If the axis of the parabola touches a circle of radius r having AB as its diameter, then the slope of the line joining A and B can be
A
2r
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B
−2r
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C
1r
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D
−1r
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Solution
The correct option is B−2r
Mid-point of A&B a(t1+t2)=r t1+t2=ra
Slope of AB=2a(t1−t2)(t21−t22)=2t1+t2=2ar
In y2=4x a=1 ∴ slope =2r
If circle is below x−axis, then
Slope =−2r