Medium MCQ +4 / -1 PYQ · JEE Mains 2021

Let [x] denote the greatest integer less than or equal to x. Then, the values of x$\in$R satisfying the equation ${[{e^x}]^2} + [{e^x} + 1] - 3 = 0$ lie in the interval :

  1. A $\left[ {0,{1 \over e}} \right)$
  2. B [log<sub>e</sub>2, log<sub>e</sub>3)
  3. C [1, e)
  4. D [0, log<sub>e</sub>2) Correct answer

Solution

${[{e^x}]^2} + [{e^x} + 1] - 3 = 0$<br><br>$\Rightarrow {[{e^x}]^2} + [{e^x}] + 1 - 3 = 0$<br><br>Let $[{e^x}] = t$<br><br>$\Rightarrow {t^2} + t - 2 = 0$<br><br>$\Rightarrow t = - 2,1$<br><br>$[{e^x}] = - 2$ (Not possible)<br><br>or $[{e^x}] = 1$ $\therefore$ $1 \le {e^x} &lt; 2$<br><br>$\Rightarrow \ln (1) \le x &lt; \ln (2)$<br><br>$\Rightarrow 0 \le x &lt; \ln (2)$<br><br>$\Rightarrow x \in [0,\ln 2)$

About this question

Subject: Mathematics · Chapter: Complex Numbers and Quadratic Equations · Topic: Complex Numbers and Argand Plane

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