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Questions  

 Let y=3x8 be the equation of the tangent at the point  (7, 13) lying on a parabola whose focus is at (1,1) . The 

 length of the latus rectum of the parabola is 

a
2013
b
2013
c
1013
d
2065

detailed solution

Correct option is D

The image of focus (−1,−1) upon the tangent y=3x−8 is the point (5,−3) . It will lie on the directrix.  Slope of directrix =−7−513+3=−18Its equation isy+3=−18(x−5) or  x+8y+19=0∴  Latus rectum =2×( Distance of focus from directrix )=2×|−1−8+19|65=2065

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