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JEE Main 202229 JulyEvening Shift
Exam
JEE Main
Year
2022
Date
29 July
Shift
Evening Shift
Subject
Mathematics
Chapter
Differential Equations

JEE Main 2022 · 29 July · Evening Shift · Mathematics · Differential Equations

Let y = y(x) be the solution curve of the differential equation...

Let y=y(x)y = y\left(x\right) be the solution curve of the differential equation dydx+(2x2+11x+13x3+6x2+11x+6)y=(x+3)x+1,x>−1\dfrac{dy}{dx} + \left(\dfrac{2{x}^{2} + 11x + 13}{{x}^{3} + 6{x}^{2} + 11x + 6}\right)y = \dfrac{\left(x + 3\right)}{x + 1}, x > - 1, which passes through the point \left(0, 1\right).Then. Theny\left(1\right) is equal to

Options

  1. A12\dfrac{1}{2}
  2. B32\dfrac{3}{2}
  3. C52\dfrac{5}{2}
  4. D72\dfrac{7}{2}

Correct answer

B. 32\dfrac{3}{2}

Step-by-step solution

Given,

dydx+(2x2+11x+13x3+6x2+11x+6)y=x+3x+1\dfrac{dy}{dx} + \left(\dfrac{2{x}^{2} + 11x + 13}{{x}^{3} + 6{x}^{2} + 11x + 6}\right)y = \dfrac{x + 3}{x + 1}

Now comparing with dydx+y×p(x)=q(x)\dfrac{dy}{dx} + y \times p\left(x\right) = q\left(x\right)
We get p(x)=2x2+11x+13x3+6x2+11x+6p\left(x\right) = \dfrac{2{x}^{2} + 11x + 13}{{x}^{3} + 6{x}^{2} + 11x + 6}

So IF=e∫2x2+11x+13x3+6x2+11x+6dxIF = {e}^{∫ \dfrac{2{x}^{2} + 11x + 13}{{x}^{3} + 6{x}^{2} + 11x + 6}dx}

Now finding the integration we get,

∫p(x)dx=∫(2x2+11x+13)dx(x+1)(x+2)(x+3)∫ p\left(x\right)dx = ∫ \dfrac{\left(2{x}^{2} + 11x + 13\right)dx}{\left(x + 1\right)\left(x + 2\right)\left(x + 3\right)}

Using partial fraction we get,

2x2+11x+13(x+1)(x+2)(x+3)=Ax+1+Bx+2+Cx+3\dfrac{2{x}^{2} + 11x + 13}{\left(x + 1\right)\left(x + 2\right)\left(x + 3\right)} = \dfrac{A}{x + 1} + \dfrac{B}{x + 2} + \dfrac{C}{x + 3}

On solving we get A = 42=\dfrac{4}{2} =2,,B = 1 and C = - 1</p><p>So,</p><p>So,∫ p\left(x\right)dx=Aln(x+1)dx = Aln\left(x + 1\right) + Bln\left(x + 2\right)+cln(x+3)+ cln\left(x + 3\right)

= \ln \left(\dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{x + 3}\right)</p><p>So,</p><p>So,IF = {e}^{∫ p\left(x\right)dx} = \dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{\left(x + 3\right)}</p><p>Nowsolutionofdifferentialequationisgivenby</p><p></p><p>Now solution of differential equation is given by</p><p>y \times IF = ∫ Q \times IFdx</p><p></p><p>⇒ y \times \left(\dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{x + 3}\right) = ∫ \left(\dfrac{x + 3}{x + 1}\right)\dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{\left(x + 3\right)}dx</p><p></p><p>⇒ y \times \left(\dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{x + 3}\right) = \dfrac{{x}^{3}}{3} + \dfrac{3{x}^{2}}{2} + 2x + c</p><p>Nowgivencurvepassesthrough(0,1)</p><p>Now given curve passes through \left(0, 1\right),

So, ⇒1×((0+1)2(0+2)0+3)=033+3×022+2×0+c⇒c=23⇒ 1 \times \left(\dfrac{{\left(0 + 1\right)}^{2}\left(0 + 2\right)}{0 + 3}\right) = \dfrac{{0}^{3}}{3} + \dfrac{3 \times {0}^{2}}{2} + 2 \times 0 + c ⇒ c = \dfrac{2}{3}

So, curve becomes y×((x+1)2(x+2)x+3)=x33+3x22+2x+23y \times \left(\dfrac{{\left(x + 1\right)}^{2}\left(x + 2\right)}{x + 3}\right) = \dfrac{{x}^{3}}{3} + \dfrac{3{x}^{2}}{2} + 2x + \dfrac{2}{3}

Now put x=1x = 1 we get, y×((1+1)2(1+2)1+3)=133+3×122+2×1+23y \times \left(\dfrac{{\left(1 + 1\right)}^{2}\left(1 + 2\right)}{1 + 3}\right) = \dfrac{{1}^{3}}{3} + \dfrac{3 \times {1}^{2}}{2} + 2 \times 1 + \dfrac{2}{3}

⇒y×3=1+32+2⇒y×3=92⇒ y \times 3 = 1 + \dfrac{3}{2} + 2 ⇒ y \times 3 = \dfrac{9}{2}

⇒y(1)=32⇒ y\left(1\right) = \dfrac{3}{2}

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