Let y = y(x), x > 1, be the solution of the differential equation $(x - 1){{dy} \over {dx}} + 2xy = {1 \over {x - 1}}$, with $y(2) = {{1 + {e^4}} \over {2{e^4}}}$. If $y(3) = {{{e^\alpha } + 1} \over {\beta {e^\alpha }}}$, then the value of $\alpha + \beta$ is equal to _________.
Answer (integer)
14
Solution
$\frac{d y}{d x}+y\left(\frac{2 x}{x-1}\right)=\frac{1}{(x-1)^{2}}$
<br/><br/>
$\text { I.F} =e^{\int \frac{2 x}{x-1} d x}$
<br/><br/>
$$
\begin{aligned}
& =e^{2 \int\left(\frac{x-1}{x-1}+\frac{1}{x-1}\right) d x} \\\\
& =e^{2 x+2 \ln (x-1)} \\\\
& =\mathrm{e}^{2 x}(\mathrm{x}-1)^{2}
\end{aligned}
$$
<br/><br/>
$\Rightarrow \int d\left(y \cdot e^{2 x}(x-1)^{2}\right)=\int e^{2 x} d x$
<br/><br/>
$\Rightarrow \quad y \cdot e^{2 x}(x-1)^{2}=\frac{e^{2 x}}{2}+c$
<br/><br/>
$\downarrow y(2)=\frac{1+e^{4}}{2 e^{4}}$
<br/><br/>
$\frac{1+e^{4}}{2 e^{4}} \cdot e^{4}=\frac{e^{4}}{2}+c$
<br/><br/>
$\Rightarrow \quad c=\frac{e^{4}}{2}\left(\frac{1+e^{4}-e^{4}}{e^{4}}\right)=\frac{1}{2}$
<br/><br/>
$\Rightarrow \quad y \cdot e^{2 x}(x-1)^{2}=\frac{e^{2 x}+1}{2}$
<br/><br/>
$\downarrow y(3)=\frac{e^{\alpha}+1}{\beta e^{\alpha}}$
<br/><br/>
$\Rightarrow \frac{e^{\alpha}+1}{\beta e^{\alpha}} \cdot e^{6} \cdot 4=\frac{e^{6}+1}{2}$
<br/><br/>
$\Rightarrow \alpha=6$ and $\beta=8 \Rightarrow \alpha+\beta=14$
About this question
Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree
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