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JEE Main 201912 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
12 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Differentiation

JEE Main 2019 · 12 April · Morning Shift · Mathematics · Differentiation

If e ^ y + xy = e, the ordered pair ((dy)/(dx), d ^ 2 y d x ^ 2 )...

If ey+xy=e,{e}^{y} + xy = e, the ordered pair (dydx,d2ydx2)\left(\dfrac{dy}{dx}, \dfrac{{d}^{2}y}{d{x}^{2}}\right) at x=0x = 0 is equal to

Options

  1. A(−1e,−1e2)\left(- \dfrac{1}{e}, - \dfrac{1}{{e}^{2}}\right)
  2. B(−1e,1e2)\left(- \dfrac{1}{e}, \dfrac{1}{{e}^{2}}\right)
  3. C(1e,−1e2)\left(\dfrac{1}{e}, - \dfrac{1}{{e}^{2}}\right)
  4. D(1e,1e2)\left(\dfrac{1}{e}, \dfrac{1}{{e}^{2}}\right)

Correct answer

B. (−1e,1e2)\left(- \dfrac{1}{e}, \dfrac{1}{{e}^{2}}\right)

Step-by-step solution

ey+xy=e{e}^{y} + xy = e

differentiate w. r. t. xx

eydydx+xdydx+y=0{e}^{y}\dfrac{dy}{dx} + x\dfrac{dy}{dx} + y = 0

⇒ \dfrac{dy}{dx}\left(x + {e}^{y}\right) = - y, {\left\dfrac{dy}{dx}\right|}_{( 0,1 )} = - \dfrac{1}{e}

Again differentiate w. r. t. xx

ey.d2ydx2+dydx.ey.dydx+x.d2ydx2+dydx+dydx=0{e}^{y} . \dfrac{{d}^{2}y}{d{x}^{2}} + \dfrac{dy}{dx} . {e}^{y} . \dfrac{dy}{dx} + x . \dfrac{{d}^{2}y}{d{x}^{2}} + \dfrac{dy}{dx} + \dfrac{dy}{dx} = 0

⇒(x+ey)d2ydx2+(dydx)2.ey+2dydx=0⇒ \left(x + {e}^{y}\right)\dfrac{{d}^{2}y}{d{x}^{2}} + {\left(\dfrac{dy}{dx}\right)}^{2} . {e}^{y} + 2\dfrac{dy}{dx} = 0

Now, at \left(0, 1\right)</p><p></p><p>e\dfrac{{d}^{2}y}{d{x}^{2}} + \dfrac{1}{{e}^{2}}e + 2\left(- \dfrac{1}{e}\right) = 0</p><p></p><p>∴ \dfrac{{d}^{2}y}{d{x}^{2}} = \dfrac{1}{{e}^{2}}</p><p>Hence,orderedpair(dydx,d2ydx2)=(−1e,1e2)</p><p>Hence, ordered pair \left(\dfrac{dy}{dx}, \dfrac{{d}^{2}y}{d{x}^{2}}\right) = \left(- \dfrac{1}{e}, \dfrac{1}{{e}^{2}}\right)

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