Double ordinate AB of the parabola y2=4ax subtends an angle π2 at the vertex of the parabola, then tangents drawn to parabola at A and B will intersect at
A
(−4a,0)
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B
(−2a,0)
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C
(−3a,0)
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D
None of these
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Solution
The correct option is C(−4a,0) Let A≡(at2,2at),B≡(at2,−2at). mOA=2t,mOB=−2t Thus, (2t)(−2t)=−1 ⇒t2=4 Equation of tangent through A is yt=x+at2 Equation of tangent through B is −yt=x+at2 ⇒x=−at2 ⇒x=−4a ⇒y=0 Thus, tangents will intersect at (−4a,0).