Question Details

Let R denote the set of all real numbers. Then the area of the region
{ ( x , y ) R × R : x > 0 , y > 1 x , 5 x 4 y 1 > 0 , 4 x + 4 y 17 < 0 } is

Options

A

17 16 log e 4

B

33 8 log e 4

C

57 8 log e 4

D

17 2 log e 4

Show Answer

Correct Answer :

Option B

33 8 log e 4

Solution :

The correct answer is:
33 8 - log e 4

Step-by-Step Derivation:

Let the region be denoted by S. We are given the inequalities defining the region:
1) x>0
2) y>1x
3) 5x-4y-1>0y<5x-14
4) 4x+4y-17<0y<17-4x4

First, we find the intersection points of the boundary curves to identify the limits of integration.

1. Intersection of the two straight lines:
5x-14 = 17-4x4
5x-1 = 17 - 4 x
9x = 18 x = 2
At x=2, we have y=94.

2. Intersection of the line y=5x-14 and the hyperbola y=1x:
5x-14 = 1x
5x2 - x - 4 = 0
(5x+4) (x-1) = 0
Since x>0, we take x=1.

3. Intersection of the line y=17-4x4 and the hyperbola y=1x:
17-4x4 = 1x
4x2 - 17x + 4 = 0
(4x-1) (x-4) = 0
This gives x=14 and x=4. Because x=2 is the transition boundary, the region lies in the interval [1,4].

We split the required area A into two parts:
- From x=1 to x=2, where the region is bounded below by y=1x and above by y=5x-14.
- From x=2 to x=4, where the region is bounded below by y=1x and above by y=17-4x4.

Calculating the area integrals:
A = 1 2 5x-14 - 1x dx + 2 4 17-4x4 - 1x dx

First Integral:
I1 = 5x28 - x4 - lnx 1 2
I1 = 208 - 24 - ln2 - 58 - 14 - 0
I1 = 2 - ln2 - 38 = 138 - ln2

Second Integral:
I2 = 17x4 - x22 - lnx 2 4
I2 = 17 - 8 - ln4 - 344 - 2 - ln2
I2 = 9 - 2ln2 - 132 - ln2
I2 = 52 - ln2

Summing the two parts to get the total area:
A = I1 + I2
A = 138 - ln2 + 52 - ln2
A = 138 + 208 - 2ln2
A = 338 - loge4

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