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JEE Main 202431 JanuaryMorning Shift
Exam
JEE Main
Year
2024
Date
31 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Limits

JEE Main 2024 · 31 January · Morning Shift · Mathematics · Limits

Let a be the sum of all coefficients in the expansion of ( 1 – 2x +...

Let aa be the sum of all coefficients in the expansion of (1–2x+2x2)2023(3−4x2+2x3)2024( 1 – 2x + 2{x}^{2}{)}^{2023} ( 3 - 4{x}^{2} + 2{x}^{3}{)}^{2024} and b=lim⁡x→0(∫0xlog⁡(1+t)t2024+1dtx2)b = \lim_{x \to 0}\left(\dfrac{{∫}_{0}^{x}\dfrac{\log \left(1 + t\right)}{{t}^{2024} + 1}dt}{{x}^{2}}\right). If the equations cx2+dx+e=0c{x}^{2} + dx + e = 0 and 2bx2+ax+4=02b{x}^{2} + ax + 4 = 0 have a common root, where c,d,e∈Rc, d, e \in R, then d:c:ed: c: e equals

Options

  1. A2:1:42: 1: 4
  2. B4:1:44: 1: 4
  3. C1:2:41: 2: 4
  4. D1:1:41: 1: 4

Correct answer

D. 1:1:41: 1: 4

Step-by-step solution

Given: aa is the sum of all coefficients in (1−2x+2x2)2023(3−4x2+2x3)2024{\left(1 - 2x + 2{x}^{2}\right)}^{2023}{\left(3 - 4{x}^{2} + 2{x}^{3}\right)}^{2024}

⇒a=(1−2×1+2×1)2023(3−4×1+2×1)2024⇒ a = {\left(1 - 2 \times 1 + 2 \times 1\right)}^{2023}{\left(3 - 4 \times 1 + 2 \times 1\right)}^{2024}

⇒a=1...(i)⇒ a = 1 . . . \left(i\right)

Now, b=lim⁡x→0∫0xlog⁡(1+t)t2024+1dtx2b = \lim_{x \to 0}\dfrac{{∫}_{0}^{x}\dfrac{\log \left(1 + t\right)}{{t}^{2024} + 1}dt}{{x}^{2}}

Using L-Hospital's rule and Newton Leibnitz Theorem, we get

⇒b=lim⁡x→0log⁡(1+x)(x2024+1)2x⇒ b = \lim_{x \to 0}\dfrac{\log \left(1 + x\right)}{\left({x}^{2024} + 1\right)2x}

⇒b=lim⁡x→012(x2024+1)⇒ b = \lim_{x \to 0}\dfrac{1}{2\left({x}^{2024} + 1\right)}

⇒b=12...(ii)⇒ b = \dfrac{1}{2} . . . \left(ii\right)

Also, 2bx2+ax+4=02b{x}^{2} + ax + 4 = 0

⇒x2+x+4=0⇒ {x}^{2} + x + 4 = 0, which gives complex conjugates as roots.

Let αandα\alpha\text{and} \alpha be those roots.

Then, cx2+dx+e=0c{x}^{2} + dx + e = 0 will also have αandα\alpha\text{and} \alpha as roots.

⇒d:c:e=1:1:4⇒ d: c: e = 1: 1: 4

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