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JEE Main 202126 FebruaryEvening Shift
Exam
JEE Main
Year
2021
Date
26 February
Shift
Evening Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2021 · 26 February · Evening Shift · Mathematics · Differential Equations

Let slope of the tangent line to a curve at any point P(x, y) be...

Let slope of the tangent line to a curve at any point P(x,y)P\left(x, y\right) be given by xy2+yx\dfrac{x{y}^{2} + y}{x}. If the curve intersects the line x+2y=4x + 2y = 4 at x=−2x = - 2, then the value of yy, for which the point \left(3, y\right)$ lies on the curve, is :

Options

  1. A−43- \dfrac{4}{3}
  2. B1835\dfrac{18}{35}
  3. C−1819- \dfrac{18}{19}
  4. D−1811- \dfrac{18}{11}

Correct answer

C. −1819- \dfrac{18}{19}

Step-by-step solution

Given dydx=xy2+yx\dfrac{dy}{dx} = \dfrac{x{y}^{2} + y}{x}

xdy−ydxy2=xdx\dfrac{xdy - ydx}{{y}^{2}} = xdx

−d(xy)=xdx- d\left(\dfrac{x}{y}\right) = xdx

−xy=x22+c- \dfrac{x}{y} = \dfrac{{x}^{2}}{2} + c

∵∵ Curve intersects the line x+2y=4x + 2y = 4 at x=−2⇒x = - 2 ⇒ point of intersection is (−2,3)\left(- 2, 3\right).

∴∴ Curve passes through \left(- 2, 3\right).</p><p>. </p><p>⇒ \dfrac{2}{3} = 2 + c ⇒ c = - \dfrac{4}{3}</p><p></p><p>⇒ \dfrac{- x}{y} = \dfrac{{x}^{2}}{2} - \dfrac{4}{3}</p><p>Nowput(3,y)</p><p>Now put \left(3, y\right) we get,

⇒−3y=196⇒ \dfrac{- 3}{y} = \dfrac{19}{6}

⇒y=−1819⇒ y = \dfrac{- 18}{19}

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