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Area Under the Curves question

2025 · 24 Jan · Shift 2 · Q30
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  5. /2025 · 24 Jan · Shift 2 · Q30

Area Under the Curves question

2025 · 24 Jan · Shift 2 · Q30

JEE MainMathematicsArea Under the CurvesMCQ+4 / −1
The area of the region enclosed by the curves y=ex,y=∣ex−1∣y=\mathrm{e}^x, y=\left|\mathrm{e}^x-1\right|y=ex,y=∣ex−1∣ and yyy-axis is :
  1. A
    1+log⁡e21+\log _{\mathrm{e}} 21+loge​2
  2. B
    log⁡e2\log _{\mathrm{e}} 2loge​2
  3. C
    1−log⁡e21-\log _{\mathrm{e}} 21−loge​2
  4. D
    2log⁡e2−12 \log _{\mathrm{e}} 2-12loge​2−1
View written solutionFree

Correct answer: C

  1. Understand the curves

We are given:

  • y=exy=e^xy=ex
  • y=∣ex−1∣y=|e^x-1|y=∣ex−1∣
  • the yyy-axis, i.e. x=0x=0x=0

We first simplify ∣ex−1∣|e^x-1|∣ex−1∣ depending on xxx.

Since ex<1e^x<1ex<1 for x<0x<0x<0, we get ∣ex−1∣=1−ex(x<0).|e^x-1|=1-e^x \qquad (x<0).∣ex−1∣=1−ex(x<0).

Since ex≥1e^x\ge 1ex≥1 for x≥0x\ge 0x≥0, we get ∣ex−1∣=ex−1(x≥0).|e^x-1|=e^x-1 \qquad (x\ge 0).∣ex−1∣=ex−1(x≥0).

Because the region is enclosed with the yyy-axis (x=0x=0x=0), the enclosed part must lie to the left of the yyy-axis, i.e. for x≤0x\le 0x≤0.

So in the relevant region, the curves are:

  • upper curve: y=exy=e^xy=ex
  • lower curve: y=1−exy=1-e^xy=1−ex
  1. Find their point of intersection

Set ex=1−ex.e^x=1-e^x.ex=1−ex. So, 2ex=12e^x=12ex=1 ex=12e^x=\frac12ex=21​ x=ln⁡(12)=−ln⁡2.x=\ln\left(\frac12\right)=-\ln 2.x=ln(21​)=−ln2.

Thus the two curves intersect at x=−ln⁡2.x=-\ln 2.x=−ln2.

At x=0x=0x=0:

  • y=e0=1y=e^0=1y=e0=1
  • y=∣e0−1∣=0y=|e^0-1|=0y=∣e0−1∣=0

Hence the region enclosed by the two curves and the line x=0x=0x=0 lies for −ln⁡2≤x≤0.-\ln 2 \le x \le 0.−ln2≤x≤0.

  1. Set up the area integral

Area A=∫−ln⁡20[ex−(1−ex)]dx.A=\int_{-\ln 2}^{0} \left[e^x-(1-e^x)\right]dx.A=∫−ln20​[ex−(1−ex)]dx.

Simplify the integrand: ex−(1−ex)=2ex−1.e^x-(1-e^x)=2e^x-1.ex−(1−ex)=2ex−1.

So, A=∫−ln⁡20(2ex−1) dx.A=\int_{-\ln 2}^{0} (2e^x-1)\,dx.A=∫−ln20​(2ex−1)dx.

  1. Evaluate the integral

∫(2ex−1)dx=2ex−x.\int (2e^x-1)dx=2e^x-x.∫(2ex−1)dx=2ex−x.

Therefore, A=[2ex−x]−ln⁡20.A=\left[2e^x-x\right]_{-\ln 2}^{0}.A=[2ex−x]−ln20​.

At x=0x=0x=0: 2e0−0=2.2e^0-0=2.2e0−0=2.

At x=−ln⁡2x=-\ln 2x=−ln2: 2e−ln⁡2−(−ln⁡2)=2⋅12+ln⁡2=1+ln⁡2.2e^{-\ln 2}-(-\ln 2)=2\cdot \frac12+\ln 2=1+\ln 2.2e−ln2−(−ln2)=2⋅21​+ln2=1+ln2.

Hence, A=2−(1+ln⁡2)=1−ln⁡2.A=2-(1+\ln 2)=1-\ln 2.A=2−(1+ln2)=1−ln2.

  1. Match with options

A=1−ln⁡2A=1-\ln 2A=1−ln2 which corresponds to Option C.

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