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JEE Main 201419 AprilOnline
Exam
JEE Main
Year
2014
Date
19 April
Mode
Online
Subject
Mathematics
Chapter
Indefinite Integration

JEE Main 2014 · 19 April · Online · Mathematics · Indefinite Integration

If m is a non-zero number and ∫ x ^ 5m - 1 + 2 x ^ 4m - 1 ( x ^ 2m...

If mm is a non-zero number and ∫x5m−1+2x4m−1(x2m+xm+1)3∫ \dfrac{{x}^{5m - 1} + 2{x}^{4m - 1}}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{3}}dx = f(x)+c,\left(x\right) + c, then f(x)f\left(x\right) is equal to

Options

  1. A\dfrac{\left({x}^{5m} - {x}^{4m}\right)}{2m{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}}
  2. B\dfrac{1}{2m}\dfrac{{x}^{4m}}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}}
  3. C\dfrac{{x}^{5m}}{2m{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}}
  4. D\dfrac{2m\left({x}^{5m} + {x}^{4m}\right)}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}}

Correct answer

B. \dfrac{1}{2m}\dfrac{{x}^{4m}}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}}

Step-by-step solution

∫x5m−1+2x4m−1(x2m+xm+1)3dx=f(x)+c∫ \dfrac{{x}^{5m - 1} + 2{x}^{4m - 1}}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{3}}dx = f\left(x\right) + c

⇒∫x5m−1+2x4m−1x6m(1+x−m+x−2m)3dx=f(x)+c⇒ ∫ \dfrac{{x}^{5m - 1} + 2{x}^{4m - 1}}{{x}^{6m}{\left(1 + {x}^{- m} + {x}^{- 2m}\right)}^{3}}dx = f\left(x\right) + c

⇒∫x−m−1+2x−2m−1(1+x−m+x−2m)3dx=f(x)+c⇒ ∫ \dfrac{{x}^{- m - 1} + 2{x}^{- 2m - 1}}{{\left(1 + {x}^{- m} + {x}^{- 2m}\right)}^{3}}dx = f\left(x\right) + c.

If, 1+x−m+x−2m=t1 + {x}^{- m} + {x}^{- 2m} = t

⇒−m(x−m−1+2x−2m−1)dx=dt⇒ - m\left({x}^{- m - 1} + 2{x}^{- 2m - 1}\right)dx = dt

∴∫−dtmt3=f(x)+c∴ ∫ \dfrac{- dt}{m{t}^{3}} = f\left(x\right) + c

⇒−1m∫t−3dt=f(x)+c⇒ - \dfrac{1}{m} ∫ {t}^{- 3}dt = f\left(x\right) + c

Using ∫xndx=xn+1n+1+C,n≠−1∫ {x}^{n}dx = \dfrac{{x}^{n + 1}}{n + 1} + C, n \ne - 1

⇒−1m(t−2−2)=f(x)+c⇒ - \dfrac{1}{m}\left(\dfrac{{t}^{- 2}}{- 2}\right) = f\left(x\right) + c

⇒12m(1+x−m+x−2m)2+c=f(x)+c⇒ \dfrac{1}{2m{\left(1 + {x}^{- m} + {x}^{- 2m}\right)}^{2}} + c = f\left(x\right) + c

⇒12m(1+1xm+1x2m)2+c=f(x)+c⇒ \dfrac{1}{2m{\left(1 + \dfrac{1}{{x}^{m}} + \dfrac{1}{{x}^{2m}}\right)}^{2}} + c = f\left(x\right) + c

⇒12mx4m(x2m+xm+1)2=f(x).⇒ \dfrac{1}{2m}\dfrac{{x}^{4m}}{{\left({x}^{2m} + {x}^{m} + 1\right)}^{2}} = f\left(x\right) .

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