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JEE Advanced 2019Paper 1
Exam
JEE Advanced
Year
2019
Paper
Paper 1
Subject
Mathematics
Chapter
Area Under Curves

JEE Advanced 2019 · Paper 1 · Mathematics · Area Under Curves

The area of the region \ (x, y): xy ≤ 8, 1 ≤ y ≤ x ^ 2 \ is

The area of the region {(x,y): xy ≤8,1≤y≤x2}\left\{\left(x, y\right):\text{ xy } \le 8, 1 \le y \le {x}^{2}\right\} isThe area of the region \ (x, y): xy ≤ 8, 1 ≤ y ≤ x ^ 2 \ is

Options

  1. A16log⁡e2−14316\log_{e} 2 - \dfrac{14}{3}
  2. B8log⁡e2−738\log_{e} 2 - \dfrac{7}{3}
  3. C8log⁡e2−1438\log_{e} 2 - \dfrac{14}{3}
  4. D16log⁡e2−616\log_{e} 2 - 6

Correct answer

A. 16log⁡e2−14316\log_{e} 2 - \dfrac{14}{3}

Step-by-step solution

The area of the region \ (x, y): xy ≤ 8, 1 ≤ y ≤ x ^ 2 \ is
To draw the inequality, let us draw the equation
xy=8xy = 8 and y=1y = 1 and y=x2y = {x}^{2}
For point of intersection
(i) xy=8xy = 8 and y=1⇒A(8,1)y = 1 ⇒ A ( 8,1 )
(ii) xy=8xy = 8 and y=x2⇒x3=8⇒x=2⇒B(2,4)y = {x}^{2} ⇒ {x}^{3} = 8 ⇒ x = 2 ⇒ B ( 2, 4 )
(iii) y=x2andy = {x}^{2} andy = 1 ⇒ C(1,1)C\left(1, 1\right) and D(1,1)D\left(1, 1\right)
Now xy≤8⇒xy \le 8 ⇒ region which contains origin
y≥1⇒y \ge 1 ⇒ region above line y=1y = 1
y≤x2⇒y \le {x}^{2} ⇒ region outside the parabola
Now required area
Method I:
Using x-axis:
A=∫12(x2−1)⋅dx+∫28(8x−1)⋅dxA = \mathop{∫}_{1}^{2}\left({x}^{2} - 1\right) ⋅ dx + \mathop{∫}_{2}^{8}\left(\dfrac{8}{x} - 1\right) ⋅ dx
A=[x33−x]12+[8ln⁡x−x]28A = {\left[\dfrac{{x}^{3}}{3} - x\right]}_{1}^{2} + {\left[8\ln x - x\right]}_{2}^{8}
A=−143+16ln⁡2A = - \dfrac{14}{3} + 16\ln 2
Method II:
Using y-axis:
A=∫14(8y−y)⋅dyA = \mathop{∫}_{1}^{4}\left(\dfrac{8}{y} - \sqrt{y}\right) ⋅ dy
A=[8ln⁡y−23y32]14⇒A=−143+16ln⁡2A = {\left[8\ln y - \dfrac{2}{3}{y}^{\dfrac{3}{2}}\right]}_{1}^{4} ⇒ A = - \dfrac{14}{3} + 16\ln 2
Note: The question should include bounded area term as in 2nd{2}^{nd} quadrant there exist a area which satisfy the inequality and is unbounded.
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