Medium MCQ +4 / -1 PYQ · JEE Mains 2023

Let $\mathrm{y}=f(x)$ represent a parabola with focus $\left(-\frac{1}{2}, 0\right)$ and directrix $y=-\frac{1}{2}$. Then

$$S=\left\{x \in \mathbb{R}: \tan ^{-1}(\sqrt{f(x)})+\sin ^{-1}(\sqrt{f(x)+1})=\frac{\pi}{2}\right\}$$ :

  1. A is an empty set
  2. B contains exactly one element
  3. C contains exactly two elements Correct answer
  4. D is an infinite set

Solution

$\left(x+\frac{1}{2}\right)^{2}=\left(y+\frac{1}{4}\right)$ <br/><br/>$y=\left(x^{2}+x\right)$ <br/><br/>$\tan ^{-1} \sqrt{\mathrm{x}(\mathrm{x}+1)}+\sin ^{-1} \sqrt{\mathrm{x}^{2}+\mathrm{x}+1}=\pi / 2$ <br/><br/>$0 \leq \mathrm{x}^{2}+\mathrm{x}+1 \leq 1$ <br/><br/>$x^{2}+x \leq 0$ <br/><br/>Also $x^{2}+x \geq 0$ <br/><br/>$\therefore \mathrm{x}^{2}+\mathrm{x}=0 \Rightarrow \mathrm{x}=0,-1$ <br/><br/>$\mathrm{S}$ contains 2 element.

About this question

Subject: Mathematics · Chapter: Conic Sections · Topic: Parabola

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