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+1 vote
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in Mathematics by (47.3k points)
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Let y = y(x) be the solution of the differential equation 

\(\left(2 x \log _{e} x\right) \frac{d y}{d x}+2 y=\frac{3}{x} \log _{e} x, x>0 \) and \( y\left(e^{-1}\right)=\) 0. Then, y(e) is equal to 

(1) \(-\frac{3}{2 \mathrm{e}}\)

(2) \(-\frac{2}{3 \mathrm{e}}\)

(3) \(-\frac{3}{\mathrm{e}}\)

(4) \(-\frac{2}{\mathrm{e}}\)

1 Answer

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by (49.3k points)
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Best answer

Correct option is (3) \(-\frac{3}{\mathrm{e}}\)

\(\frac{\mathrm{dy}}{\mathrm{dx}}+\frac{\mathrm{y}}{\mathrm{x} \ln \mathrm{x}}=\frac{3}{2 \mathrm{x}^{2}}\)

\(\therefore I.F. =\mathrm{e}^{\int \frac{1}{x \ln x} \mathrm{dx}}=\mathrm{e}^{\ln (\ln (\mathrm{x}))}=\ln \mathrm{x}\)

\(\therefore \mathrm{y} \ell \mathrm{nx}=\int \frac{3 \ln \mathrm{x}}{2 \mathrm{x}^{2}} \mathrm{dx}\)

\(=\frac{3 \ln x}{2} \int x^{-2} d x-\int\left(\frac{3}{2 x} \cdot \int x^{-2} d x\right) d x\)

\(=\frac{3 \ln \mathrm{x}}{2}\left(-\frac{1}{\mathrm{x}}\right)-\int \frac{3}{2 \mathrm{x}}\left(-\frac{1}{\mathrm{x}}\right) \mathrm{dx}\)

\( y. \ln x=\frac{-3 \ln x}{2 x}-\frac{3}{2 x}+C\)

\(\because y\left(\mathrm{e}^{-1}\right)=0\)

\(\therefore 0(-1)=\frac{3 \mathrm{e}}{2}-\frac{3 \mathrm{e}}{2}+\mathrm{C} \Rightarrow \mathrm{C}=0\)

\(\therefore \mathrm{y}=\frac{-3 \ln \mathrm{x}}{2 \mathrm{x}}-\frac{3}{2 \mathrm{x}}\)

\(\therefore y(e)=\frac{-3}{2 e}-\frac{3}{2 e}=\frac{-3}{e}\)

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