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JEE Main 202131 AugustEvening Shift
Exam
JEE Main
Year
2021
Date
31 August
Shift
Evening Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2021 · 31 August · Evening Shift · Mathematics · Differential Equations

If (dy)/(dx) = 2 ^ x y + 2 ^ y · 2 ^ x 2 ^ x + 2 ^ x + y _ e 2 ,...

If dydx=2xy+2y⋅2x2x+2x+ylog⁡e2,y(0)=0,\dfrac{dy}{dx} = \dfrac{{2}^{x}y + {2}^{y} \cdot {2}^{x}}{{2}^{x} + {2}^{x + y}\log_{e}2}, y\left(0\right) = 0, then for y=1,y = 1, the value of xx lies in the interval :

Options

  1. A(1,2)\left(1, 2\right)
  2. B(12,1]\left(\dfrac{1}{2}, 1\right]
  3. C(2,3)\left(2, 3\right)
  4. D(0,12]\left(0, \dfrac{1}{2}\right]

Correct answer

A. (1,2)\left(1, 2\right)

Step-by-step solution

Given differential equation is

dydx=2x⋅y+2y⋅2x2x+2x+ylog⁡e2\dfrac{dy}{dx} = \dfrac{{2}^{x} \cdot y + {2}^{y} \cdot {2}^{x}}{{2}^{x} + {2}^{x + y}\log_{e}2}

⇒dydx=2x(y+2y)2x(1+2ylog⁡e2)⇒ \dfrac{dy}{dx} = \dfrac{{2}^{x}\left(y + {2}^{y}\right)}{{2}^{x}\left(1 + {2}^{y}\log_{e}2\right)}

⇒∫1+2ylog⁡e2y+2ydy=∫dx⇒ ∫ \dfrac{1 + {2}^{y}\log_{e}2}{y + {2}^{y}}dy = ∫ dx

⇒∫d(y+2y)y+2y=∫dx⇒ ∫ \dfrac{d\left(y + {2}^{y}\right)}{y + {2}^{y}} = ∫ dx

⇒ln⁡∣y+2y∣=x+C[∵∫f′(x)f(x)dx=ln⁡(f(x))+C]⇒ \ln \left|y + {2}^{y}\right| = x + C\left[∵ ∫ \dfrac{{f}^{'}\left(x\right)}{f\left(x\right)}dx = \ln \left(f\left(x\right)\right) + C\right]

Now ∵y(0)=0∵ y\left(0\right) = 0

⇒C=0⇒ C = 0

∴ln⁡∣y+2y∣=x∴ \ln \left|y + {2}^{y}\right| = x

Now for y=1y = 1 we have

x=ln⁡(1+2)=ln⁡3∈(1,2)x = \ln \left(1 + 2\right) = \ln 3 \in \left(1, 2\right)

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