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JEE Main 201910 AprilMorning Shift
Exam
JEE Main
Year
2019
Date
10 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Indefinite Integration

JEE Main 2019 · 10 April · Morning Shift · Mathematics · Indefinite Integration

If ∫ dx ( x ^ 2 - 2x + 10) ^ 2 = A( ^ - 1 ((x - 1)/(3)) + f(x) x ^...

If ∫dx(x2−2x+10)2=A(tan⁡−1(x−13)+f(x)x2−2x+10)+C∫ \dfrac{dx}{{\left({x}^{2} - 2x + 10\right)}^{2}} = A\left(\tan^{- 1}\left(\dfrac{x - 1}{3}\right) + \dfrac{f\left(x\right)}{{x}^{2} - 2x + 10}\right) + C, then (where CC is a constant of integration)

Options

  1. AA = \dfrac{1}{27}andandf\left(x\right) = 9\left(x - 1\right)
  2. BA = \dfrac{1}{81}andandf\left(x\right) = 3\left(x - 1\right)
  3. CA=154A = \dfrac{1}{54} and ff\left(x\right) = 9{\left(x - 1\right)}^{2}
  4. DA = \dfrac{1}{54}andandf\left(x\right) = 3\left(x - 1\right)

Correct answer

D. A = \dfrac{1}{54}andandf\left(x\right) = 3\left(x - 1\right)

Step-by-step solution

We have I=∫dx(x2−2x+10)2=∫dx[(x−1)2+32]2I = ∫ \dfrac{dx}{{\left({x}^{2} - 2x + 10\right)}^{2}} = ∫ \dfrac{dx}{{\left[{\left(x - 1\right)}^{2} + {3}^{2}\right]}^{2}}

Let x–1=3tanθ⇒dx=3sec⁡2\thetadθx – 1 = 3tan\theta ⇒ dx = 3\sec^{2}\thetad\theta

⇒I=∫3sec2\thetadθ81sec4θ=127∫cos2\thetadθ⇒ I = ∫ \dfrac{3se{c}^{2}\thetad\theta}{81se{c}^{4}\theta} = \dfrac{1}{27} ∫ co{s}^{2}\thetad\theta

=154∫(1+cos⁡2θ)dθ= \dfrac{1}{54} ∫ \left(1 + \cos 2\theta\right)d\theta

=154(θ+sin⁡2θ2)+C= \dfrac{1}{54}\left(\theta + \dfrac{\sin 2\theta}{2}\right) + C

=154(θ+sinθcosθ)+C= \dfrac{1}{54}\left(\theta + sin\theta cos\theta\right) + C, where CC is the constant of integration.

=154[tan⁡−1(x−13)+(x−13)1+(x−13)2]+C= \dfrac{1}{54}\left[\tan^{- 1}\left(\dfrac{x - 1}{3}\right) + \dfrac{\left(\dfrac{x - 1}{3}\right)}{1 + {\left(\dfrac{x - 1}{3}\right)}^{2}}\right] + C

=154[tan−1(x−13)+3(x−1)x2−2x+10]+C= \dfrac{1}{54}\left[ta{n}^{- 1}\left(\dfrac{x - 1}{3}\right) + \dfrac{3\left(x - 1\right)}{{x}^{2} - 2x + 10}\right] + C

Hence, A=154 and f(x)=3(x−1)A = \dfrac{1}{54} \text{ and } f\left(x\right) = 3 ( x - 1 )

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