Mathematics · Application of Derivatives

JEE Main 2026 — 24 January, Evening Shift — Question 2

Let the length of the latus rectum of an ellipse x2a2+y2b2=1,(a>b)\frac{x^{2}}{a^{2}}+\frac{y^{2}}{b^{2}}=1,(a>b), be 30 . If its eccentricity is the maximum value of the function f(t)=−34+2t−t2f(t)=-\frac{3}{4}+2 t-t^{2}, then (a2+b2)\left(\mathrm{a}^{2}+\mathrm{b}^{2}\right) is equal to -

  1. Option A:

    516

  2. Option B:

    256

  3. Option C:

    496

    Correct
  4. Option D:

    276

Answer: C

Step-by-step solution

f(t)=−34+2t−t2f(t)=\frac{-3}{4}+2 t-t^{2} f(t)∣maximum =14=e⇒e2=116⇒a2−b2a2=116\begin{gathered} \left.f(t)\right|_{\text {maximum }}=\frac{1}{4}=e \Rightarrow e^{2}=\frac{1}{16} \Rightarrow \frac{a^{2}-b^{2}}{a^{2}}=\frac{1}{16} \end{gathered}

∵2 b2a=30⇒ b2=15a\begin{gathered} \because \frac{2 \mathrm{~b}^{2}}{\mathrm{a}}=30 \Rightarrow \mathrm{~b}^{2}=15 \mathrm{a} \end{gathered}

By & (2) 16(a2−15a)=a2⇒15a2−16×15a=016\left(a^{2}-15 a\right)=a^{2} \Rightarrow 15 a^{2}-16 \times 15 a=0

a=16\mathrm{a}=16 b2=240\mathrm{b}^{2}=240

a2+b2=256+240\mathrm{a}^{2}+\mathrm{b}^{2}=256+240

=496=496

Answer key and solution verified before publishing.

Practise Application of Derivatives

Start with this question, then two more from the same chapter — with a tutor that explains every step. Free.

Exam
JEE Main 2026
Subject
Mathematics
Chapter
Application of Derivatives
Topic
Maxima and Minima
Let the length of the latus rectum of an ellipse frac x 2 a 2 +frac y… | JEE Main 2026 PYQ with Solution · DhiX AI