JEE MAIN - Mathematics (2023 - 11th April Evening Shift - No. 12)
Let $$y=y(x)$$ be the solution of the differential equation $$\frac{d y}{d x}+\frac{5}{x\left(x^{5}+1\right)} y=\frac{\left(x^{5}+1\right)^{2}}{x^{7}}, x > 0$$. If $$y(1)=2$$, then $$y(2)$$ is equal to :
$$\frac{693}{128}$$
$$\frac{697}{128}$$
$$\frac{637}{128}$$
$$\frac{679}{128}$$
Explanation
I.F $=\mathrm{e}^{\int \frac{5 \mathrm{dx}}{\mathrm{x}\left(\mathrm{x}^5+1\right)}}=\mathrm{e}^{\int \frac{5 \mathrm{x}^{-6} \mathrm{dx}}{\left(\mathrm{x}^{-5}+1\right)}}$
Put, $1+\mathrm{x}^{-5}=\mathrm{t} \Rightarrow-5 \mathrm{x}^{-6} \mathrm{dx}=\mathrm{dt}$
$$ \therefore $$ $$ e^{\int-\frac{d t}{t}}=e^{-\ln t}=\frac{1}{t}=\frac{x^5}{1+x^5} $$
$$ \begin{aligned} y \cdot \frac{x^5}{1+x^5} & =\int \frac{x^5}{\left(1+x^5\right)} \times \frac{\left(1+x^5\right)^2}{x^7} d x \\\\ & =\int x^3 d x+\int x^{-2} d x \end{aligned} $$
$$ y \cdot \frac{x^5}{1+x^5}=\frac{x^4}{4}-\frac{1}{x}+c $$
$$ \text { Given that: } x=1 \Rightarrow y=2 $$
$$ \begin{aligned} & 2 \cdot \frac{1}{2}=\frac{1}{4}-1+\mathrm{c} \\\\ & \mathrm{c}=\frac{7}{4} \\\\ & \mathrm{y} \cdot \frac{\mathrm{x}^5}{1+\mathrm{x}^5}=\frac{\mathrm{x}^4}{4}-\frac{1}{\mathrm{x}}+\frac{7}{4} \\\\ & \text { Now put, } \mathrm{x}=2 \\\\ & \mathrm{y} \cdot\left(\frac{32}{33}\right)=\frac{21}{4} \\\\ & \mathrm{y}=\frac{693}{128} \end{aligned} $$
Put, $1+\mathrm{x}^{-5}=\mathrm{t} \Rightarrow-5 \mathrm{x}^{-6} \mathrm{dx}=\mathrm{dt}$
$$ \therefore $$ $$ e^{\int-\frac{d t}{t}}=e^{-\ln t}=\frac{1}{t}=\frac{x^5}{1+x^5} $$
$$ \begin{aligned} y \cdot \frac{x^5}{1+x^5} & =\int \frac{x^5}{\left(1+x^5\right)} \times \frac{\left(1+x^5\right)^2}{x^7} d x \\\\ & =\int x^3 d x+\int x^{-2} d x \end{aligned} $$
$$ y \cdot \frac{x^5}{1+x^5}=\frac{x^4}{4}-\frac{1}{x}+c $$
$$ \text { Given that: } x=1 \Rightarrow y=2 $$
$$ \begin{aligned} & 2 \cdot \frac{1}{2}=\frac{1}{4}-1+\mathrm{c} \\\\ & \mathrm{c}=\frac{7}{4} \\\\ & \mathrm{y} \cdot \frac{\mathrm{x}^5}{1+\mathrm{x}^5}=\frac{\mathrm{x}^4}{4}-\frac{1}{\mathrm{x}}+\frac{7}{4} \\\\ & \text { Now put, } \mathrm{x}=2 \\\\ & \mathrm{y} \cdot\left(\frac{32}{33}\right)=\frac{21}{4} \\\\ & \mathrm{y}=\frac{693}{128} \end{aligned} $$
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