A ray of light through (2,1) is reflected at a point P on the y- axis and then passes through the point (5,3). If this reflected ray is the directrix…
JEE Main 2021 — Mathematics Coordinate Geometry
2021mcqhard
A ray of light through (2,1) is reflected at a point P on the y− axis and then passes through the point (5,3). If this reflected ray is the directrix of an ellipse with eccentricity 31 and the distance of the nearer focus from this directrix is 538, then the equation of the other directrix can be:
Official previous-year question
Held on 27 Jul 2021 · Verified 6 Jul 2026.
Options
A
11x+7y+8=0 or 11x+7y−15=0
B
11x−7y−8=0 or 11x+7y+15=0
C
2x−7y+29=0 or 2x−7y−7=0
D
2x−7y−39=0 or 2x−7y−7=0
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Solution
The reflected point of (2,1) is (−2,1).
Equation of reflected ray
y−1=5+23−1(x+2)
⇒y−1=72(x+2)
⇒7y−7=2x+4
⇒2x−7y+11=0
Let the equation of other directrix is
2x−7y+λ=0
Distance of directrix from focus
ea−ae=538, where e is the eccentricity
⇒3a−3a=538 or a=533
Distance from other focus ea+ae
=3a+3a=310a=310×533=5310
Distance between two directrix =e2a
=2×3×533=5318
So, ∣53λ−11∣=5318
⇒λ−11=18 or −18
⇒2x−7y−7=0 or 2x−7y+29=0
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