MCQMediumJEE 2025Applications of Integrals (Area)

JEE Mathematics 2025 Question with Solution

The area of the region {(x,y):x2+4x+2yx+2}\{ (x, y) : x^2 + 4x + 2 \leq y \leq |x| + 2 \} is equal to:

  • A

    77

  • B

    245\frac{24}{5}

  • C

    203\frac{20}{3}

  • D

    55

Answer

Correct answer:C

Step-by-step solution

Standard Method

Given: The region is defined by x2+4x+2yx+2x^2 + 4x + 2 \leq y \leq |x| + 2.

Find: The area enclosed between the two curves.

The solution states that the upper curve is y=x+2y = |x| + 2 and the lower curve is y=x2+4x+2y = x^2 + 4x + 2.

Write x|x| piecewise:

x={x,x<0x,x0|x| = \begin{cases} -x, & x < 0 \\ x, & x \ge 0 \end{cases}

So the curve y=x+2y = |x| + 2 becomes y=x+2y = -x + 2 for x<0x < 0 and y=x+2y = x + 2 for x0x \ge 0.

Find the intersection points as shown in the extracted working.

For the left branch,

x2+4x+2=x+2x^2 + 4x + 2 = -x + 2

which gives

x2+5x=0x^2 + 5x = 0

so

x(x+5)=0x(x+5)=0

and hence x=5x=-5 or x=0x=0.

For the right-side form used in the working,

x2+4x+2=x+2x^2 + 4x + 2 = x + 2

which gives

x2+3x=0x^2 + 3x = 0

so

x(x+3)=0x(x+3)=0

and hence x=3x=-3 or x=0x=0.

Using the interval stated in the solution, split the area as

Area=53[(x+2)(x2+4x+2)]dx+30[(x+2)(x2+4x+2)]dx\text{Area} = \int_{-5}^{-3} \left[(-x+2) - (x^2 + 4x + 2)\right] \, dx + \int_{-3}^{0} \left[(x+2) - (x^2 + 4x + 2)\right] \, dx

First integral:

53[(x+2)(x2+4x+2)]dx=53(x25x)dx\int_{-5}^{-3} \left[(-x+2) - (x^2 + 4x + 2)\right] \, dx = \int_{-5}^{-3} (-x^2 - 5x) \, dx =[x335x22]53= \left[-\frac{x^3}{3} - \frac{5x^2}{2}\right]_{-5}^{-3}

Second integral:

30[(x+2)(x2+4x+2)]dx=30(x23x)dx\int_{-3}^{0} \left[(x+2) - (x^2 + 4x + 2)\right] \, dx = \int_{-3}^{0} (-x^2 - 3x) \, dx =[x333x22]30= \left[-\frac{x^3}{3} - \frac{3x^2}{2}\right]_{-3}^{0}

According to the solution, after evaluating and summing these contributions, the final area is

203\frac{20}{3}

Therefore, the correct option is C.

Note: the second provided approach refers to x+2|x+2|, which does not match the question text. The first approach matches the given question, so it is used to determine the answer.

Common mistakes

  • Using x+2|x|+2 as a single formula over the whole interval is incorrect. The modulus must be split into branches: use x+2-x+2 for x<0x<0 and x+2x+2 for x0x\ge 0.

  • Finding intersection points without checking the sign condition for the modulus branch leads to invalid roots. After solving each equation, keep only the roots that belong to that branch's interval.

  • Subtracting the curves in the wrong order gives a negative integral. For area, integrate upper curve minus lower curve on each subinterval.

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