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JEE Main 202311 AprilEvening Shift
Exam
JEE Main
Year
2023
Date
11 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Definite Integration

JEE Main 2023 · 11 April · Evening Shift · Mathematics · Definite Integration

Let the function f: [0, 2] → ℝ be defined as f(x) = \ cases e ^...

Let the function f:[0,2]→Rf: \left[0, 2\right] \to \mathbb{R} be defined as f\left(x\right) = \left\{\begin{cases}{e}^{min\left\{{x}^{2}, x - \left[x\right]\right\}}, & x \in [ 0, 1 ) \\ {e}^{\left[x - \log_{e}x\right]}, & x \in \left[1, 2\right]\end{cases}\right), where\left[t\right]denotesthegreatestintegerlessthanorequaltodenotes the greatest integer less than or equal tot.Thenthevalueoftheintegral. Then the value of the integral{∫}_{0}^{2}xf(x)dx\left(x\right)dx is

Options

  1. A1+3e21 + \dfrac{3e}{2}
  2. B(e−1)(e2+12)\left(e - 1\right)\left({e}^{2} + \dfrac{1}{2}\right)
  3. C2e−12e - 1
  4. D2e−122e - \dfrac{1}{2}

Correct answer

D. 2e−122e - \dfrac{1}{2}

Step-by-step solution

Given,

f\left(x\right) = \left\{\begin{cases}{e}^{min\left\{{x}^{2}, x - \left[x\right]\right\}}, & x \in [ 0, 1 ) \\ {e}^{\left[x - \log_{e}x\right]}, & x \in \left[1, 2\right]\end{cases}\right)<br />⇒ f\left(x\right) = \left\{{ex2x∈[0,1)e,x∈[1,2]\begin{cases}{e}^{{x}^{2}} & x \in [ 0, 1 ) \\ e, & x \in \left[1, 2\right]\end{cases}\right)

As x−ln⁡x∈[1,2)x - \ln x \in [ 1, 2 ) for x∈[1,2]x \in [ 1, 2 ], so\left[x - \ln x\right] = 1 and x−[x]={x}x - \left[x\right] = \left\{x\right\}, so x∈(0,1),x2<{x}x \in \left(0, 1\right), {x}^{2} < \left\{x\right\}

Now solving the integral we get,∫02xf(x)=∫01x⋅ex2dx+∫12x⋅edx{∫}_{0}^{2}xf\left(x\right) = {∫}_{0}^{1}x \cdot {e}^{{x}^{2}}dx + {∫}_{1}^{2}x \cdot edx

Now in first integral, let x2=t⇒2xdx=dt{x}^{2} = t ⇒ 2xdx = dt we get,

⇒∫02xf(x)=[12∫01etdt]+[e⋅x22]12⇒ {∫}_{0}^{2}xf\left(x\right) = \left[\dfrac{1}{2}{∫}_{0}^{1}{e}^{t}dt\right] + {\left[e \cdot \dfrac{{x}^{2}}{2}\right]}_{1}^{2}

⇒∫02xf(x)=(e−12)+3e2⇒ {∫}_{0}^{2}xf\left(x\right) = \left(\dfrac{e - 1}{2}\right) + \dfrac{3e}{2}

⇒∫02xf(x)=2e−12⇒ {∫}_{0}^{2}xf\left(x\right) = 2e - \dfrac{1}{2}

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