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JEE Main 20231 FebruaryMorning Shift
Exam
JEE Main
Year
2023
Date
1 February
Shift
Morning Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2023 · 1 February · Morning Shift · Mathematics · Differential Equations

If y = y(x) is the solution curve of the differential equation...

If y=y(x)y = y\left(x\right) is the solution curve of the differential equation dydx+ytanx=xsecx,0≤x≤π3,y(0)=1\dfrac{dy}{dx} + ytanx = xsecx, 0 \le x \le \dfrac{\pi}{3}, y\left(0\right) = 1, then y(π6)y\left(\dfrac{\pi}{6}\right) is equal to

Options

  1. Aπ12−32log⁡e(2e3)\dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2}{e\sqrt{3}}\right)
  2. Bπ12+32log⁡e(23e)\dfrac{\pi}{12} + \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2\sqrt{3}}{e}\right)
  3. Cπ12−32log⁡e(23e)\dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2\sqrt{3}}{e}\right)
  4. Dπ12+32log⁡e(2e3)\dfrac{\pi}{12} + \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2}{e\sqrt{3}}\right)

Correct answer

A. π12−32log⁡e(2e3)\dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2}{e\sqrt{3}}\right)

Step-by-step solution

Given:

dydx+ytanx=xsecx\dfrac{dy}{dx} + ytanx = xsecx

This is a linear differential equation.

I.F.=e∫tanxdx=sec⁡xI . F . = {e}^{∫ tanxdx} = \sec x

Then solution of differential equation is

y(sec⁡x)=∫xsec2xdxy\left(\sec x\right) = ∫ x{sec}^{2}xdx

⇒y(sec⁡x)=xtanx−∫tanxdx⇒ y\left(\sec x\right) = xtanx - ∫ tanxdx

⇒y(sec⁡x)=xtanx−ln⁡(sec⁡x)+C⇒ y\left(\sec x\right) = xtanx - \ln \left(\sec x\right) + C

Given:

y(0)=1⇒c=1y\left(0\right) = 1 ⇒ c = 1

∴y(sec⁡x)=xtanx−ln⁡(sec⁡x)+1∴ y\left(\sec x\right) = xtanx - \ln \left(\sec x\right) + 1

At x=π6x = \dfrac{\pi}{6}, we get

y(sec⁡(π6))=(π6)tan⁡(π6)−ln⁡(sec⁡(π6))+1y\left(\sec \left(\dfrac{\pi}{6}\right)\right) = \left(\dfrac{\pi}{6}\right)\tan \left(\dfrac{\pi}{6}\right) - \ln \left(\sec \left(\dfrac{\pi}{6}\right)\right) + 1

⇒y(23)=(π6)(13)−ln⁡(23)+1⇒ y\left(\dfrac{2}{\sqrt{3}}\right) = \left(\dfrac{\pi}{6}\right)\left(\dfrac{1}{\sqrt{3}}\right) - \ln \left(\dfrac{2}{\sqrt{3}}\right) + 1

⇒y=π12−32ln⁡(23)+32⇒ y = \dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\ln \left(\dfrac{2}{\sqrt{3}}\right) + \dfrac{\sqrt{3}}{2}

⇒y=π12−32[ln⁡(23)−lne]⇒ y = \dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\left[\ln \left(\dfrac{2}{\sqrt{3}}\right) - lne\right]

⇒y=π12−32log⁡e(2e3)⇒ y = \dfrac{\pi}{12} - \dfrac{\sqrt{3}}{2}\log_{e}\left(\dfrac{2}{e\sqrt{3}}\right)

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