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JEE Main 202622 JanuaryEvening Shift
Exam
JEE Main
Year
2026
Date
22 January
Shift
Evening Shift
Subject
Mathematics
Chapter
Ellipse

JEE Main 2026 · 22 January · Evening Shift · Mathematics · Ellipse

Let S and S^ be the foci of the ellipse x^ 2 25 + y^ 2 9 =1 and...

Let S and S′\mathrm{S}^{\prime} be the foci of the ellipse x225+y29=1\frac{x^{2}}{25}+\frac{y^{2}}{9}=1 and P(α,β)\mathrm{P}(\alpha, \beta) be a point on the ellipse in the first quadrant. If (SP)2+(S′P)2−SP⋅S′P=37(\mathrm{SP})^{2}+\left(\mathrm{S}^{\prime} \mathrm{P}\right)^{2}-\mathrm{SP} \cdot \mathrm{S}^{\prime} \mathrm{P}=37, then α2+β2\alpha^{2}+\beta^{2} is equal to :

Options

  1. A15
  2. B11
  3. C17
  4. D13

Correct answer

D. 13

Step-by-step solution

For the ellipse x225+y29=1\frac{x^2}{25} + \frac{y^2}{9} = 1, we have a=5a = 5, b=3b = 3, c=4c = 4.
So foci are at S(±4,0)S(\pm 4, 0).
For point PP on the ellipse: SP+S′P=10SP + S'P = 10.
Given (SP)2+(S′P)2−SP⋅S′P=37(SP)^2 + (S'P)^2 - SP \cdot S'P = 37
Let r1=SPr_1 = SP and r2=S′Pr_2 = S'P.
From (r1+r2)2=100(r_1 + r_2)^2 = 100, we get r12+r22=100−2r1r2r_1^2 + r_2^2 = 100 - 2r_1r_2.
Substituting into the given equation: 100−3r1r2=37100 - 3r_1r_2 = 37, so r1r2=21r_1r_2 = 21.
Thus r1=3,r2=7r_1 = 3, r_2 = 7.
From (α+4)2+β2=9(\alpha + 4)^2 + \beta^2 = 9 and (α−4)2+β2=49(\alpha - 4)^2 + \beta^2 = 49, subtracting gives 16α=−4016\alpha = -40, so α=−52\alpha = -\frac{5}{2}.
From the ellipse equation: β2=274\beta^2 = \frac{27}{4}.
Therefore α2+β2=254+274=13\alpha^2 + \beta^2 = \frac{25}{4} + \frac{27}{4} = 13.
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