If the solution curve $f(x, y)=0$ of the differential equation
$\left(1+\log _{e} x\right) \frac{d x}{d y}-x \log _{e} x=e^{y}, x > 0$,
passes through the points $(1,0)$ and $(\alpha, 2)$, then $\alpha^{\alpha}$ is equal to :
Solution
We have, $\left(1+\log _e x\right) \frac{d x}{d y}-x \log _e x=e^{y}, x>0$
<br/><br/>Put $x \log _e x=t$
<br/><br/>$$
\begin{aligned}
& \Rightarrow \left(x \cdot \frac{1}{x}+\log _e x\right) \frac{d x}{d y} =\frac{d t}{d y} \\\\
& \Rightarrow \left(1+\log _e x\right) \frac{d x}{d y} =\frac{d t}{d y} \\\\
& \therefore \frac{d t}{d y}-t =e^{y}
\end{aligned}
$$
<br/><br/>Now, IF $=e^{\int-d y}=e^{-y}$
<br/><br/>$\begin{aligned} & \therefore \text { General solution, } t\left(e^{-y}\right)=\int\left(e^y \cdot e^{-y}\right) d y+c \\\\ & \Rightarrow t e^{-y}=\int d y+c \\\\ & \Rightarrow t e^{-y}=y+c \\\\ & \Rightarrow \left(x \log _e x\right) e^{-y}=y+c ..........(i)\end{aligned}$
<br/><br/>Equation (i), passes through the point $(1,0)$
<br/><br/>$$
\begin{aligned}
& \therefore 0=0+c \\\\
& \Rightarrow c=0 \\\\
& \therefore \left(x \log _e x\right) e^{-y}=y \\\\
& \Rightarrow x \log _e x=y e^y
\end{aligned}
$$
<br/><br/>Which passes through $(\alpha, 2)$
<br/><br/>$$
\begin{aligned}
& \therefore \alpha \log _e \alpha=2 e^2 \\\\
& \Rightarrow \log _e \alpha^\alpha=2 e^2 \\\\
& \Rightarrow \alpha^\alpha=e^{2 e^2}
\end{aligned}
$$
About this question
Subject: Mathematics · Chapter: Differential Equations · Topic: Order and Degree
This question is part of PrepWiser's free JEE Main question bank. 172 more solved questions on Differential Equations are available — start with the harder ones if your accuracy is >70%.