MCQMediumJEE 2025Applications of Integrals (Area)

JEE Mathematics 2025 Question with Solution

The area (in sq. units) of the region (x,y):0y2x+1,0yx2+1,x3(x, y) : 0 \leq y \leq 2|x| + 1, 0 \leq y \leq x^2 + 1, |x| \leq 3 is:

  • A

    643\frac{64}{3}

  • B

    173\frac{17}{3}

  • C

    323\frac{32}{3}

  • D

    803\frac{80}{3}

Answer

Correct answer:A

Step-by-step solution

Standard Method

Given: The region is defined by

0y2x+10 \leq y \leq 2|x| + 1 0yx2+10 \leq y \leq x^2 + 1 x3|x| \leq 3

Find: The area of the region.

The region is symmetric about the yy-axis, so calculate the area for x0x \geq 0 and multiply by 22.

For x0x \geq 0, the upper boundary is

ymin(2x+1,x2+1),0x3y \leq \min(2x + 1, x^2 + 1), \qquad 0 \leq x \leq 3

Find the intersection points by equating the two curves:

x2+1=2x+1x^2 + 1 = 2x + 1 x22x=0x^2 - 2x = 0 x=0 or x=2x = 0 \text{ or } x = 2

Now compare the curves:

  • For 0x20 \leq x \leq 2, x2+12x+1x^2 + 1 \leq 2x + 1
  • For 2x32 \leq x \leq 3, 2x+1x2+12x + 1 \leq x^2 + 1

So the first-quadrant area is

02(x2+1)dx+23(2x+1)dx\int_0^2 (x^2 + 1) \, dx + \int_2^3 (2x + 1) \, dx

Evaluate the integrals:

02(x2+1)dx+23(2x+1)dx\int_0^2 (x^2 + 1) \, dx + \int_2^3 (2x + 1) \, dx =[x33+x]02+[x2+x]23= \left[ \frac{x^3}{3} + x \right]_0^2 + \left[ x^2 + x \right]_2^3 =(83+2)+(9+3)(4+2)= \left(\frac{8}{3} + 2\right) + (9 + 3) - (4 + 2) =143+6=323= \frac{14}{3} + 6 = \frac{32}{3}

Using symmetry, total area is

2×323=6432 \times \frac{32}{3} = \frac{64}{3}

Therefore, the correct option is A and the area is 643\frac{64}{3}.

Symmetry and piecewise boundary

Given: The region lies below both y=2x+1y = 2|x| + 1 and y=x2+1y = x^2 + 1, above y=0y = 0, with x3|x| \leq 3.

Find: The enclosed area.

Because both expressions involve x|x| or x2x^2, the region is symmetric about the yy-axis. Hence,

Area=2×(area in the first quadrant part)\text{Area} = 2 \times \text{(area in the first quadrant part)}

In the first quadrant, x=x|x| = x, so the two upper curves become y=2x+1y = 2x + 1 and y=x2+1y = x^2 + 1. The relevant upper boundary is the smaller of these two curves.

Their intersection is obtained from

x2+1=2x+1x^2 + 1 = 2x + 1 x22x=0x^2 - 2x = 0 x(x2)=0x(x-2) = 0

Thus, they meet at x=0x = 0 and x=2x = 2.

So the area in the first quadrant is split into two parts:

02(x2+1)dx+23(2x+1)dx\int_0^2 (x^2 + 1) \, dx + \int_2^3 (2x + 1) \, dx

The first integral is

[x33+x]02=83+2=143\left[\frac{x^3}{3} + x\right]_0^2 = \frac{8}{3} + 2 = \frac{14}{3}

The second integral is

[x2+x]23=(9+3)(4+2)=6\left[x^2 + x\right]_2^3 = (9+3) - (4+2) = 6

Hence first-quadrant area is

143+6=323\frac{14}{3} + 6 = \frac{32}{3}

Therefore, total area is

2323=6432 \cdot \frac{32}{3} = \frac{64}{3}

Therefore, the area of the region is 643\frac{64}{3}.

Common mistakes

  • Using the larger upper curve instead of the smaller one. The inequalities require yy to satisfy both upper bounds, so the correct ceiling is min(2x+1,x2+1)\min(2|x|+1, x^2+1), not the maximum.

  • Forgetting symmetry about the yy-axis. If you integrate only for x0x \geq 0 and do not multiply by 22, you get only half the required area.

  • Not splitting the integral at the intersection point x=2x = 2. The lower of the two curves changes there, so one single integral over 00 to 33 is incorrect.

Practice more Applications of Integrals (Area) questions

Get unlimited AI-adaptive practice, mastery tracking, and an AI tutor that explains every step — free to start.

Related questions