JEE MAIN - Mathematics (2023 - 29th January Evening Shift - No. 1)
Let $$y=y(x)$$ be the solution of the differential equation $$x{\log _e}x{{dy} \over {dx}} + y = {x^2}{\log _e}x,(x > 1)$$. If $$y(2) = 2$$, then $$y(e)$$ is equal to
$${{1 + {e^2}} \over 2}$$
$${{1 + {e^2}} \over 4}$$
$${{2 + {e^2}} \over 2}$$
$${{4 + {e^2}} \over 4}$$
Explanation
$$x\ln x{{dy} \over {dx}} + y = {x^2}\ln x$$
$${{dy} \over {dx}} + {1 \over {x\ln x}}\,.\,y = x$$
If $$ = {e^{\int {{1 \over {x\ln x}}dx} }} = {e^{\int {{1 \over t}dt} }}$$, where $$t = \ln x$$
$$ = {e^{\ln t}} = t = \ln x$$
$$y.\ln x = \int {x\ln x = {{{x^2}} \over 2}\ln x - \int {{{{x^2}} \over 2}\,.\,{1 \over x}} } $$
$$y\ln x = {{{x^2}} \over 2}\ln x - {{{x^2}} \over 4} + C$$ ..... (i)
$$y(2) = 2 \Rightarrow C = 1$$
Putting $$x = e$$ in (i),
$$y = {{{e^2}} \over 4} + 1 = {{4 + {e^2}} \over 4}$$
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