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JEE Main 202315 AprilMorning Shift
Exam
JEE Main
Year
2023
Date
15 April
Shift
Morning Shift
Subject
Mathematics
Chapter
Definite Integration

JEE Main 2023 · 15 April · Morning Shift · Mathematics · Definite Integration

If ∫ _ 0 ^ 1 1 (5 + 2x - 2 x ^ 2 )(1 + e ^ (2 - 4x) ) dx = (1)/(α)...

If ∫011(5+2x−2x2)(1+e(2−4x))dx=1αlog⁡e(α+1β),α,β>0{∫}_{0}^{1}\dfrac{1}{\left(5 + 2x - 2{x}^{2}\right)\left(1 + {e}^{\left(2 - 4x\right)}\right)}dx = \dfrac{1}{\alpha}\log_{e}\left(\dfrac{\alpha + 1}{\beta}\right), \alpha, \beta > 0, then α4−β4{\alpha}^{4} - {\beta}^{4} is equal to

Options

  1. A1919
  2. B−21- 21
  3. C00
  4. D2121

Correct answer

D. 2121

Step-by-step solution

Given,

∫011(5+2x−2x2)(1+e(2−4x))dx=1αlog⁡e(α+1β){∫}_{0}^{1}\dfrac{1}{\left(5 + 2x - 2{x}^{2}\right)\left(1 + {e}^{\left(2 - 4x\right)}\right)}dx = \dfrac{1}{\alpha}\log_{e}\left(\dfrac{\alpha + 1}{\beta}\right)

Now let,

I=12∫011(52−(x2−x))(1+e−4(x−12))dxI = \dfrac{1}{2}{∫}_{0}^{1}\dfrac{1}{\left(\dfrac{5}{2} - \left({x}^{2} - x\right)\right)\left(1 + {e}^{- 4\left(x - \dfrac{1}{2}\right)}\right)}dx

⇒I=12∫011((114)−(x−12)2)(1+e−4(x−12))dx⇒ I = \dfrac{1}{2}{∫}_{0}^{1}\dfrac{1}{\left(\left(\dfrac{11}{4}\right) - {\left(x - \dfrac{1}{2}\right)}^{2}\right)\left(1 + {e}^{- 4\left(x - \dfrac{1}{2}\right)}\right)}dx

Now let x−12=t⇒dx=dtx - \dfrac{1}{2} = t ⇒ dx = dt

So, integral becomes,

I=12∫−12121(112)2−t2)(1+e−4t)dtI = \dfrac{1}{2}{∫}_{\dfrac{- 1}{2}}^{\dfrac{1}{2}}\dfrac{1}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2})\left(1 + {e}^{- 4t}\right)}dt

⇒I=12∫−1201(112)2−t2)(1+e−4t)dt+12∫0121(112)2−t2)(1+e−4t)dt⏟I2⇒ I = \dfrac{1}{2}{∫}_{\dfrac{- 1}{2}}^{0}\dfrac{1}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2})\left(1 + {e}^{- 4t}\right)}dt + \mathop{\mathop{\dfrac{1}{2}{∫}_{0}^{\dfrac{1}{2}}\dfrac{1}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2})\left(1 + {e}^{- 4t}\right)}dt}_{⏟}}_{{I}_{2}}

Now solving I2=12∫−12121(112)2−t2)(1+e−4t)dt{I}_{2} = \dfrac{1}{2}{∫}_{\dfrac{- 1}{2}}^{\dfrac{1}{2}}\dfrac{1}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2})\left(1 + {e}^{- 4t}\right)}dt,

Let t=−zt = - z, we get dt=−dzdt = - dz

So, I2=−12∫120dz(112)2−z2)(1+e4z){I}_{2} = - \dfrac{1}{2}{∫}_{\dfrac{1}{2}}^{0}\dfrac{dz}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {z}^{2})\left(1 + {e}^{4z}\right)}

⇒I2=12∫012dt(112)2−t2)(1+e4t)⇒ {I}_{2} = \dfrac{1}{2}{∫}_{0}^{\dfrac{1}{2}}\dfrac{dt}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2})\left(1 + {e}^{4t}\right)}

Now putting the value of I2inI{I}_{2}\text{in}I we get,

I=12∫0121((112)2−t2)(1+e−4t)+1((112)2−t2)(1+e4t)dtI = \dfrac{1}{2}{∫}_{0}^{\dfrac{1}{2}}\dfrac{1}{\left({\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2}\right)\left(1 + {e}^{- 4t}\right)} + \dfrac{1}{\left({\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2}\right)\left(1 + {e}^{4t}\right)}dt

⇒I=12∫012e4t((112)2−t2)(e4t+1)+1((112)2−t2)(1+e4t)dt⇒ I = \dfrac{1}{2}{∫}_{0}^{\dfrac{1}{2}}\dfrac{{e}^{4t}}{\left({\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2}\right)\left({e}^{4t} + 1\right)} + \dfrac{1}{\left({\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2}\right)\left(1 + {e}^{4t}\right)}dt

⇒I=12∫0121(112)2−t2dt⇒ I = \dfrac{1}{2}{∫}_{0}^{\dfrac{1}{2}}\dfrac{1}{{\left(\dfrac{\sqrt{11}}{2}\right)}^{2} - {t}^{2}}dt

⇒I=12×12(112)[ln⁡∣112+t112−t∣]012⇒ I = \dfrac{1}{2} \times \dfrac{1}{2\left(\dfrac{\sqrt{11}}{2}\right)}{\left[\ln \left|\dfrac{\dfrac{\sqrt{11}}{2} + t}{\dfrac{\sqrt{11}}{2} - t}\right|\right]}_{0}^{\dfrac{1}{2}}

⇒I=1211ln⁡(11+111−1)=1211ln⁡((11+1)210)⇒ I = \dfrac{1}{2\sqrt{11}}\ln \left(\dfrac{\sqrt{11} + 1}{\sqrt{11} - 1}\right) = \dfrac{1}{2\sqrt{11}}\ln \left(\dfrac{( \sqrt{11} + 1{)}^{2}}{10}\right)

⇒I=111ln⁡(11+110)⇒ I = \dfrac{1}{\sqrt{11}}\ln \left(\dfrac{\sqrt{11} + 1}{\sqrt{10}}\right)

Now on comparing with 1αlog⁡e(α+1β)\dfrac{1}{\alpha}\log_{e}\left(\dfrac{\alpha + 1}{\beta}\right) we get,

⇒α=11,β=10⇒α4−β4=21⇒ \alpha = \sqrt{11}, \beta = \sqrt{10} ⇒ {\alpha}^{4} - {\beta}^{4} = 21

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