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JEE Advanced 2025 · Applications of Integrals

Let R\mathbb{R} denote the set of all real numbers. Then the area of the region {(x,y)∈R×R:x>0, y>1x, 5x−4y−1>0, 4x+4y−17<0}\{(x, y) \in \mathbb{R} \times \mathbb{R} : x > 0,\, y > \frac{1}{x},\, 5x - 4y - 1 > 0,\, 4x + 4y - 17 < 0\} is

Answer: B. 338−log⁡e4\frac{33}{8} - \log_e 4

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x>0,y>1xx > 0,\quad y > \dfrac1x 5x−4y−1>0,4x+4y−17<05x - 4y - 1 > 0,\quad 4x + 4y - 17 < 0 To find: area of the region\text{To find: area of the region} L1:y=5x−14,L2:y=17−4x4L_1: y = \dfrac{5x-1}{4},\quad L_2: y = \dfrac{17-4x}{4} H:y=1xH: y = \dfrac1x 1x<y<min⁡ ⁣(5x−14, 17−4x4)\dfrac1x < y < \min\!\left(\dfrac{5x-1}{4},\ \dfrac{17-4x}{4}\right) L1≤L2  ⟺  x≤2L_1 \le L_2 \iff x \le 2 H∩L1: x=1, y=1H \cap L_1:\ x = 1,\ y = 1 L1∩L2: x=2, y=94L_1 \cap L_2:\ x = 2,\ y = \dfrac94 H∩L2: x=4, y=14H \cap L_2:\ x = 4,\ y = \dfrac14 A=∫12 ⁣(5x−14−1x)dx+∫24 ⁣(17−4x4−1x)dxA = \int_1^2\!\left(\dfrac{5x-1}{4} - \dfrac1x\right)dx + \int_2^4\!\left(\dfrac{17-4x}{4} - \dfrac1x\right)dx ∫12 ⁣(5x−14−1x)dx=138−ln⁡2\int_1^2\!\left(\dfrac{5x-1}{4} - \dfrac1x\right)dx = \dfrac{13}{8} - \ln 2 ∫24 ⁣(17−4x4−1x)dx=52−ln⁡2\int_2^4\!\left(\dfrac{17-4x}{4} - \dfrac1x\right)dx = \dfrac52 - \ln 2 A=138+52−2ln⁡2=338−ln⁡4A = \dfrac{13}{8} + \dfrac52 - 2\ln 2 = \dfrac{33}{8} - \ln 4 338−log⁡e4(2)\boxed{\dfrac{33}{8} - \log_e 4} \quad (2)

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