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

If $${{dy} \over {dx}} = {{{2^x}y + {2^y}{{.2}^x}} \over {{2^x} + {2^{x + y}}{{\log }_e}2}}$$, y(0) = 0, then for y = 1, the value of x lies in the interval :

  1. A (1, 2) Correct answer
  2. B $\left( {{1 \over 2},1} \right]$
  3. C (2, 3)
  4. D $\left( {0,{1 \over 2}} \right]$

Solution

${{dy} \over {dx}} = {{{2^x}(y + {2^y})} \over {{2^x}(1 + {2^y}\ln 2)}}$<br><br>$\Rightarrow \int {{{(1 + {2^y})\ln 2} \over {(y + {2^y})}}dy = \int {dx} }$<br><br>$\Rightarrow \ln \left| {y + {2^y}} \right| = x + c$<br><br>x = 0; y = 0 $\Rightarrow$ c = 0<br><br>$\Rightarrow x = \ln \left| {y + {2^y}} \right|$<br><br>$\Rightarrow$ at y = 1, x = ln3<br><br>$\because$ $3 \in (e,{e^2}) \Rightarrow x \in (1,2)$

About this question

Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree

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