Question:
If $y=y(x)$ is the solution of the differential equation $\frac{5+\mathrm{e}^{\mathrm{x}}}{2+\mathrm{y}} \cdot \frac{\mathrm{dy}}{\mathrm{dx}}+\mathrm{e}^{\mathrm{x}}=0$ satisfying
$y(0)=1$, then a value of $y\left(\log _{e} 13\right)$ is :
Correct Option: , 2
Solution:
$\frac{\left(5+\mathrm{e}^{\mathrm{x}}\right)}{2+\mathrm{y}} \frac{\mathrm{dy}}{\mathrm{dx}}=-\mathrm{e}^{\mathrm{x}}$
$\int \frac{d y}{2+y}=\int \frac{-e^{x}}{e^{x}+5} d x$
$\ln (y+2)=-\ln \left(e^{x}+5\right)+k$
$(y+2)\left(e^{x}+5\right)=C$
$\because y(0)=1$
$\Rightarrow \mathrm{C}=18$
$y+2=\frac{18}{e^{x}+5}$
at $x=\ln 13$
$y+2=\frac{18}{13+5}=1$
$y=-1$
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