JEE Challenger
More from Application of Integrals

Area of Region Bounded by Hyperbola and Parabola

Find the area of the region defined by the set {(x,y):xy≤8,1≤y≤x2}\{(x,y) : xy \le 8, 1 \le y \le x^2\}.

Options

A

16log⁡e2−14316 \log_e 2 - \frac{14}{3}

Correct
B

8log⁡e2−1438 \log_e 2 - \frac{14}{3}

C

16log⁡e2−616 \log_e 2 - 6

D

8log⁡e2−738 \log_e 2 - \frac{7}{3}

Step-by-Step Solution

To find the area of the region defined by the set R={(x,y):xy≤8,1≤y≤x2}R = \{(x,y) : xy \le 8, 1 \le y \le x^2\}, we analyze the boundaries of the region in the first quadrant (where y≥1>0y \ge 1 > 0):

  1. Curves and Intersections:

    • The lower boundary of the region is given by the line y=1y = 1.
    • The upper boundary is bounded by the parabola y=x2y = x^2 and the hyperbola y=8xy = \frac{8}{x}.
    • The intersection of y=x2y = x^2 and y=1y = 1 occurs at x=1x = 1 (for x>0x > 0).
    • The intersection of y=x2y = x^2 and y=8xy = \frac{8}{x} gives x3=8  ⟹  x=2x^3 = 8 \implies x = 2.
    • The intersection of y=8xy = \frac{8}{x} and y=1y = 1 occurs at x=8x = 8.
  2. Splitting the Region into Two Parts:

    • For x∈[1,2]x \in [1, 2]: The region is bounded above by y=x2y = x^2 and below by y=1y = 1.
    • For x∈[2,8]x \in [2, 8]: The region is bounded above by y=8xy = \frac{8}{x} and below by y=1y = 1.
  3. Setting up the Definite Integrals: Area A=∫12(x2−1) dx+∫28(8x−1) dx\text{Area } A = \int_{1}^{2} (x^2 - 1) \, dx + \int_{2}^{8} \left(\frac{8}{x} - 1\right) \, dx

  4. Evaluating the First Integral: ∫12(x2−1) dx=[x33−x]12=(83−2)−(13−1)=23−(−23)=43\int_{1}^{2} (x^2 - 1) \, dx = \left[ \frac{x^3}{3} - x \right]_{1}^{2} = \left( \frac{8}{3} - 2 \right) - \left( \frac{1}{3} - 1 \right) = \frac{2}{3} - \left( -\frac{2}{3} \right) = \frac{4}{3}

  5. Evaluating the Second Integral: ∫28(8x−1) dx=[8log⁡ex−x]28=(8log⁡e8−8)−(8log⁡e2−2)\int_{2}^{8} \left(\frac{8}{x} - 1\right) \, dx = \left[ 8 \log_e x - x \right]_{2}^{8} = (8 \log_e 8 - 8) - (8 \log_e 2 - 2) =8(log⁡e8−log⁡e2)−6=8log⁡e(82)−6=8log⁡e4−6=16log⁡e2−6= 8(\log_e 8 - \log_e 2) - 6 = 8 \log_e \left(\frac{8}{2}\right) - 6 = 8 \log_e 4 - 6 = 16 \log_e 2 - 6

  6. Total Area: A=43+16log⁡e2−6=16log⁡e2−143A = \frac{4}{3} + 16 \log_e 2 - 6 = 16 \log_e 2 - \frac{14}{3}

Thus, the correct option is (A).