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Question: Answered & Verified by Expert
If $\frac{d y}{d x}=y+3>0$ and $y(0)=2$, then $y(\ln 2)$ is equal to
MathematicsDifferential EquationsJEE MainJEE Main 2011
Options:
  • A
    5
  • B
    13
  • C
    -2
  • D
    7
Solution:
1445 Upvotes Verified Answer
The correct answer is:
7
$\frac{d y}{d x}=y+3 \Rightarrow \frac{d y}{y+3}=d x$
$\ln (y+3)=x+c$
$x=0 \Rightarrow y=2$
$\Rightarrow \ln 5=0+c$
$c=\ln 5$
$\ln (y+3)=x+\ln 5$
$y+3=e^{x+\ln 5} \Rightarrow y+3=e^{\ln 2+\ln 5}$
$y+3=10 \Rightarrow y=7$

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