Mathematics · Area under the Curves

JEE Main 2024 — 4 April, Shift 1 — Question 6

One of the points of intersection of the curves y=1+3x−2x2y=1+3 x-2 x^{2} and y=1xy=\frac{1}{x} is (12,2)\left(\frac{1}{2}, 2\right).

Let the area of the region enclosed by these curves be 124(ℓ5+m)−nlog⁡e(1+5)\frac{1}{24}(\ell \sqrt{5}+\mathrm{m})-\mathrm{n} \log _{\mathrm{e}}(1+\sqrt{5}), where ℓ,m,n∈\ell, \mathrm{m}, \mathrm{n} \in N .

Then ℓ+m+n\ell+\mathrm{m}+\mathrm{n} is equal to

  1. Option A:

    32

  2. Option B:

    30

    Correct
  3. Option C:

    29

  4. Option D:

    31

Answer: B

Step-by-step solution

A=∫121+52(1+3x−2x2−1x)dxA=\int_{\frac{1}{2}}^{\frac{1+\sqrt{5}}{2}}\left(1+3 x-2 x^{2}-\frac{1}{x}\right) d x

A=[x+3x22−2x33−ln⁡x]121+52A=\left[x+\frac{3 x^{2}}{2}-\frac{2 x^{3}}{3}-\ln x\right]_{\frac{1}{2}}^{\frac{1+\sqrt{5}}{2}}

A=1+52+32(1+52)2−23(1+52)3−ln⁡(1+52)A=\frac{1+\sqrt{5}}{2}+\frac{3}{2}\left(\frac{1+\sqrt{5}}{2}\right)^{2}-\frac{2}{3}\left(\frac{1+\sqrt{5}}{2}\right)^{3}-\ln \left(\frac{1+\sqrt{5}}{2}\right)

−12−32(14)+23(18)+ln⁡(12)-\frac{1}{2}-\frac{3}{2}\left(\frac{1}{4}\right)+\frac{2}{3}\left(\frac{1}{8}\right)+\ln \left(\frac{1}{2}\right)

A=12+52+38+345+158−43−235\mathrm{A}=\frac{1}{2}+\frac{\sqrt{5}}{2}+\frac{3}{8}+\frac{3}{4} \sqrt{5}+\frac{15}{8}-\frac{4}{3}-\frac{2}{3} \sqrt{5}

−12−38+112−ln⁡(1+5)-\frac{1}{2}-\frac{3}{8}+\frac{1}{12}-\ln (1+\sqrt{5})

=5(12+34−23)+158−43+112−ln⁡(1+5)=\sqrt{5}\left(\frac{1}{2}+\frac{3}{4}-\frac{2}{3}\right)+\frac{15}{8}-\frac{4}{3}+\frac{1}{12}-\ln (1+\sqrt{5})

=14245+1524−ln⁡(1+5)=\frac{14}{24} \sqrt{5}+\frac{15}{24}-\ln (1+\sqrt{5})

ℓ+m+n=30\ell+\mathrm{m}+\mathrm{n}=30

Solution figure

Answer key and solution verified before publishing.

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Exam
JEE Main 2024
Subject
Mathematics
Chapter
Area under the Curves
Topic
Area under the Curves