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Consider the region bounded by the lines y−1=x,x=−2,x=3y - 1 = x, x = -2, x = 3 and xx - axis. Then

(A) The area of the bounded region is given by ∫−23(x+1)dx\int_{-2}^{3}(x + 1)dx

(B) The numerical value of the area is 152\frac{15}{2} sq. units

(C) The numerical value of the area is 8 sq. units

(D) The numerical value of the area is 172\frac{17}{2} sq. units

Choose the correct answer from the options given below:

Solution

✅ Correct Option: 4

The region is bounded by:

  • Line: y−1=xy - 1 = x which gives y=x+1y = x + 1
  • Left boundary: x=−2x = -2
  • Right boundary: x=3x = 3
  • Bottom: xx-axis where y=0y = 0

To find where the line crosses the xx-axis, set y=0y = 0:

0=x+10 = x + 1

x=−1x = -1

The line crosses the xx-axis at x=−1x = -1.


Checking values at key points:

At x=−2x = -2: y=−2+1=−1y = -2 + 1 = -1 (below xx-axis)

At x=−1x = -1: y=−1+1=0y = -1 + 1 = 0 (on xx-axis)

At x=3x = 3: y=3+1=4y = 3 + 1 = 4 (above xx-axis)

From x=−2x = -2 to x=−1x = -1, the line is below the xx-axis.


Checking Statement (A): Area =∫−23(x+1)dx= \int_{-2}^{3}(x + 1)dx

This is incorrect because when the curve is below the xx-axis, the integral gives a negative value, but area must be positive.

The correct formula is:

Area =∫−2−1∣x+1∣dx+∫−13(x+1)dx= \int_{-2}^{-1}|x + 1|dx + \int_{-1}^{3}(x + 1)dx

Area =∫−2−1−(x+1)dx+∫−13(x+1)dx= \int_{-2}^{-1}-(x + 1)dx + \int_{-1}^{3}(x + 1)dx

Statement (A) is incorrect.


Area below xx-axis (from x=−2x = -2 to x=−1x = -1):

∫−2−1−(x+1)dx\int_{-2}^{-1}-(x + 1)dx

=−[x22+x]−2−1= -\left[\frac{x^2}{2} + x\right]_{-2}^{-1}

At x=−1x = -1: (−1)22+(−1)=12−1=−12\frac{(-1)^2}{2} + (-1) = \frac{1}{2} - 1 = -\frac{1}{2}

At x=−2x = -2: (−2)22+(−2)=2−2=0\frac{(-2)^2}{2} + (-2) = 2 - 2 = 0

=−[−12−0]=12= -\left[-\frac{1}{2} - 0\right] = \frac{1}{2}


Area above xx-axis (from x=−1x = -1 to x=3x = 3):

∫−13(x+1)dx\int_{-1}^{3}(x + 1)dx

=[x22+x]−13= \left[\frac{x^2}{2} + x\right]_{-1}^{3}

At x=3x = 3: 92+3=152\frac{9}{2} + 3 = \frac{15}{2}

At x=−1x = -1: 12−1=−12\frac{1}{2} - 1 = -\frac{1}{2}

=152−(−12)= \frac{15}{2} - \left(-\frac{1}{2}\right)

=152+12= \frac{15}{2} + \frac{1}{2}

=162= \frac{16}{2}

=8= 8


Total Area:

Area =12+8= \frac{1}{2} + 8

Area =12+162= \frac{1}{2} + \frac{16}{2}

Area =172= \frac{17}{2} sq. units


Checking all statements:

(A) Area =∫−23(x+1)dx= \int_{-2}^{3}(x + 1)dx is incorrect

(B) Area =152= \frac{15}{2} sq. units is incorrect

(C) Area =8= 8 sq. units is incorrect

(D) Area =172= \frac{17}{2} sq. units is correct

Therefore, only statement (D) is correct.

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