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JEE Advanced 2020Paper 1
Exam
JEE Advanced
Year
2020
Paper
Paper 1
Subject
Mathematics
Chapter
Area Under Curves

JEE Advanced 2020 · Paper 1 · Mathematics · Area Under Curves

Let the functions f: R → R and g: R → R be defined by f(x) = e ^ x...

Let the functions f:R→Rf: R \to R and g:R→Rg: R \to R be defined by
f(x)=ex−1−e−∣x−1∣f\left(x\right) = {e}^{x - 1} - {e}^{- \left|x - 1\right|} and g(x)=12(ex−1+e1−x)g\left(x\right) = \dfrac{1}{2}\left({e}^{x - 1} + {e}^{1 - x}\right).
Then the area of the region in the first quadrant bounded by the curves y=f(x),y=g(x)y = f\left(x\right), y = g\left(x\right) and x=0x = 0 isLet the functions f: R → R and g: R → R be defined by f(x) = e ^ x - 1 - e ^ - |x - 1| and g(x) = (1)/(2)( e ^ x - 1 +

Options

  1. A(2−3)+12(e−e−1)\left(2 - \sqrt{3}\right) + \dfrac{1}{2}\left(e - {e}^{- 1}\right)
  2. B(2+3)+12(e−e−1)\left(2 + \sqrt{3}\right) + \dfrac{1}{2}\left(e - {e}^{- 1}\right)
  3. C(2−3)+12(e+e−1)\left(2 - \sqrt{3}\right) + \dfrac{1}{2}\left(e + {e}^{- 1}\right)
  4. D(2+3)+12(e+e−1)\left(2 + \sqrt{3}\right) + \dfrac{1}{2}\left(e + {e}^{- 1}\right)

Correct answer

A. (2−3)+12(e−e−1)\left(2 - \sqrt{3}\right) + \dfrac{1}{2}\left(e - {e}^{- 1}\right)

Step-by-step solution

f\left(x\right) = {e}^{x - 1} - {e}^{- \left|x - 1\right|} = \left\{{0,x≤1ex−1−e1−x,x>1\begin{cases}0, & x \le 1 \\ {e}^{x - 1} - {e}^{1 - x}, & x > 1\end{cases}\right) and

g(x)=12(ex−1+e1−x)g\left(x\right) = \dfrac{1}{2}\left({e}^{x - 1} + {e}^{1 - x}\right)

At x = 0, f\left(0\right) = 0 & g\left(0\right) = \dfrac{e + {e}^{- 1}}{2}

At x = 1, f\left(1\right) = 0 & g\left(1\right) = \dfrac{1}{2}\left({e}^{1 - 1} + {e}^{1 - 1}\right) = 1

For point of intersection of the two curves for x>1x > 1, f(x)=g(x)f\left(x\right) = g\left(x\right)

⇒ex−1−e1−x=12(ex−1+e1−x)⇒ {e}^{x - 1} - {e}^{1 - x} = \dfrac{1}{2}\left({e}^{x - 1} + {e}^{1 - x}\right)

⇒2ex−1−2e1−x=ex−1+e1−x⇒ 2{e}^{x - 1} - 2{e}^{1 - x} = {e}^{x - 1} + {e}^{1 - x}

⇒ex−1=3e1−x⇒ {e}^{x - 1} = 3{e}^{1 - x}

⇒(ex−1)2=3⇒ {\left({e}^{x - 1}\right)}^{2} = 3

⇒x=1+ln3⇒ x = 1 + ln\sqrt{3}

Let the functions f: R → R and g: R → R be defined by f(x) = e ^ x - 1 - e ^ - |x - 1| and g(x) = (1)/(2)( e ^ x - 1 +

∴∴Required area = Area of the shaded region

=∫01g(x)dx+∫11+ln3{g(x)−f(x)}dx= {∫}_{0}^{1}g\left(x\right)dx + {∫}_{1}^{1 + ln\sqrt{3}}\left\{g\left(x\right) - f\left(x\right)\right\}dx

=∫0112(ex−1+e1−x)dx+∫11+ln3{12(ex−1+e1−x)−(ex−1−e1−x)}dx= {∫}_{0}^{1}\dfrac{1}{2}\left({e}^{x - 1} + {e}^{1 - x}\right)dx + {∫}_{1}^{1 + ln\sqrt{3}}\left\{\dfrac{1}{2}\left({e}^{x - 1} + {e}^{1 - x}\right) - \left({e}^{x - 1} - {e}^{1 - x}\right)\right\}dx

=12∫01(ex−1+e1−x)dx+12∫11+ln3(3e1−x−ex−1)dx= \dfrac{1}{2}{∫}_{0}^{1}\left({e}^{x - 1} + {e}^{1 - x}\right)dx + \dfrac{1}{2}{∫}_{1}^{1 + ln\sqrt{3}}\left(3{e}^{1 - x} - {e}^{x - 1}\right)dx

=12[ex−1−e1−x]01−12[3e1−x+ex−1]11+ln3= \dfrac{1}{2}{\left[{e}^{x - 1} - {e}^{1 - x}\right]}_{0}^{1} - \dfrac{1}{2}{\left[3{e}^{1 - x} + {e}^{x - 1}\right]}_{1}^{1 + ln\sqrt{3}}

=12(e−e−1)−12[23−4]= \dfrac{1}{2}\left(e - {e}^{- 1}\right) - \dfrac{1}{2}\left[2\sqrt{3} - 4\right]

=e−e−12+(2−3)= \dfrac{e - {e}^{- 1}}{2} + \left(2 - \sqrt{3}\right)

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