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Let \mathrm{\mathrm{P}: y^{2}=4 a x, a>0} be a parabola with focus \mathrm{S} . Let the tangents to the parabola \mathrm{P} make an angle of \mathrm{\frac{\pi}{4}} with the line  \mathrm{y=3x+5} touch the parabola \mathrm{P} at \mathrm{A} and \mathrm{B}. Then the value of \mathrm{a} for which \mathrm{A} , \mathrm{B} and \mathrm{S} are collinear is

Option: 1

\mathrm{8\: only}


Option: 2

\mathrm{2\: only}


Option: 3

\mathrm{\frac{1}{4}\: only}


Option: 4

\mathrm{any\: a> 0}


Answers (1)

best_answer

Tangents \mathrm{T_{1}\: and\: T_{2}} make angle \mathrm{\frac{\pi}{4}} with line \mathrm{y=3x+5} means that tangents are perpendicular

Using property of parabola, point of contact of perpendicular tangents always form a focal chord. So \mathrm{A,S\: and\: B} will always be collinear for any value of \mathrm{a> 0}.

Hence the answer is option 4

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mansi

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