Question 2

SCQHARD

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,5x4y1>0,4x+4y17<0}\{(x, y) \in \mathbb{R} \times \mathbb{R} : x > 0, y > \frac{1}{x}, 5x - 4y - 1 > 0, 4x + 4y - 17 < 0\} is

(A)

1716loge4\frac{17}{16} - \log_e 4

(B)

338loge4\frac{33}{8} - \log_e 4

(C)

578loge4\frac{57}{8} - \log_e 4

(D)

172loge4\frac{17}{2} - \log_e 4

Detailed Solution

The region is bounded by:

  1. y>1xy > \frac{1}{x}
  2. y<5x14y < \frac{5x - 1}{4} (from 5x4y1>05x - 4y - 1 > 0)
  3. y<174x4y < \frac{17 - 4x}{4} (from 4x+4y17<04x + 4y - 17 < 0)

Find intersection points:

  • Between y=1xy = \frac{1}{x} and y=5x14y = \frac{5x - 1}{4}: 1x=5x14    5x2x4=0    (5x+4)(x1)=0\frac{1}{x} = \frac{5x - 1}{4} \implies 5x^2 - x - 4 = 0 \implies (5x + 4)(x - 1) = 0. Since x>0x > 0, x=1x = 1.
  • Between y=1xy = \frac{1}{x} and y=174x4y = \frac{17 - 4x}{4}: 1x=174x4    4x217x+4=0    (4x1)(x4)=0\frac{1}{x} = \frac{17 - 4x}{4} \implies 4x^2 - 17x + 4 = 0 \implies (4x - 1)(x - 4) = 0. Intersection at x=14x = \frac{1}{4} and x=4x = 4.
  • Between y=5x14y = \frac{5x - 1}{4} and y=174x4y = \frac{17 - 4x}{4}: 5x14=174x4    9x=18    x=2\frac{5x - 1}{4} = \frac{17 - 4x}{4} \implies 9x = 18 \implies x = 2.

The region lies between x=1x = 1 and x=4x = 4. For x[1,2]x \in [1, 2], upper bound is 5x14\frac{5x-1}{4}. For x[2,4]x \in [2, 4], upper bound is 174x4\frac{17-4x}{4}. The lower bound is 1x\frac{1}{x}.

Area A=12(5x141x)dx+24(174x41x)dxA = \int_1^2 \left( \frac{5x - 1}{4} - \frac{1}{x} \right) dx + \int_2^4 \left( \frac{17 - 4x}{4} - \frac{1}{x} \right) dx A=[5x28x4logex]12+[17x4x22logex]24A = \left[ \frac{5x^2}{8} - \frac{x}{4} - \log_e x \right]_1^2 + \left[ \frac{17x}{4} - \frac{x^2}{2} - \log_e x \right]_2^4 A=((20824loge2)(58140))+((178loge4)(3442loge2))A = \left( (\frac{20}{8} - \frac{2}{4} - \log_e 2) - (\frac{5}{8} - \frac{1}{4} - 0) \right) + \left( (17 - 8 - \log_e 4) - (\frac{34}{4} - 2 - \log_e 2) \right) A=(2loge238)+(92loge26.5+loge2)A = (2 - \log_e 2 - \frac{3}{8}) + (9 - 2\log_e 2 - 6.5 + \log_e 2) A=(138loge2)+(52loge2)=13+2082loge2=338loge4A = (\frac{13}{8} - \log_e 2) + (\frac{5}{2} - \log_e 2) = \frac{13 + 20}{8} - 2\log_e 2 = \frac{33}{8} - \log_e 4.

Free Exam

Boost Your Exam Preparation!

Move beyond just reading solutions. Access our comprehensive Test Series, original Mock Tests, and interactive learning modules. Many premium tests are completely free!

  • Original Mocks & Regular Test Series
  • Real NTA-like Interface with Analytics
  • Many Free Tests Available