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JEE Main 2024 · Mathematics · Differential Equations · medium

Given y(1)=1, the solution of dy/dx+y/x=x^2, evaluated at x=2, is

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Given y(1)=1y(1)=1, the solution of dydx+yx=x2\dfrac{dy}{dx}+\dfrac{y}{x}=x^2, evaluated at x=2x=2, is
  1. A. 198\dfrac{19}{8}
  2. B. 178\dfrac{17}{8}
  3. C. 94\dfrac{9}{4}
  4. D. 52\dfrac{5}{2}
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Answer: (A) 198\dfrac{19}{8}

The integrating factor is e∫dx/x=xe^{\int dx/x}=x. So ddx(xy)=x3\dfrac{d}{dx}(xy)=x^3, giving xy=x44+Cxy=\dfrac{x^4}{4}+C. Using y(1)=1y(1)=1: 1=14+C1=\tfrac14+C, C=34C=\tfrac34. At x=2x=2: 2y=4+34=1942y=4+\tfrac34=\tfrac{19}{4}, so y=198y=\tfrac{19}{8}.
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