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JEE Main 202325 JanuaryMorning Shift
Exam
JEE Main
Year
2023
Date
25 January
Shift
Morning Shift
Subject
Mathematics
Chapter
Quadratic Equation

JEE Main 2023 · 25 January · Morning Shift · Mathematics · Quadratic Equation

Let S = \ α: _ 2 ( 9 ^ 2α - 4 + 13) - _ 2 ((5)/(2) · 3 ^ 2α - 4 +...

Let
S={α:log⁡2(92α−4+13)−log⁡2(52⋅32α−4+1)=2}.S = \left\{\alpha: \log_{2}\left({9}^{2\alpha - 4} + 13\right) - \log_{2}\left(\dfrac{5}{2} \cdot {3}^{2\alpha - 4} + 1\right) = 2\right\} . Then the maximum value of β\beta for which the equation x2−2(∑α∈sα)2x+∑a∈s(α+1)2β=0{x}^{2} - 2{\left(\mathop{∑}_{\alpha \in s}\alpha\right)}^{2}x + \mathop{∑}_{a \in s}{\left(\alpha + 1\right)}^{2}\beta = 0 has real roots, is _____ .

Correct answer

0

Step-by-step solution

Given,

log⁡2(92α−4+13)−log⁡2(32α−4⋅52+1)=2\log_{2}\left({9}^{2\alpha - 4} + 13\right) - \log_{2}\left({3}^{2\alpha - 4} \cdot \dfrac{5}{2} + 1\right) = 2

Now let 32α−4=t{3}^{2\alpha - 4} = t, so the equation becomes,

log⁡2(t2+13)−log⁡2(5t2+1)=2\log_{2}\left({t}^{2} + 13\right) - \log_{2}\left(\dfrac{5t}{2} + 1\right) = 2

⇒log⁡2(t2+13)(5t2+1)=2⇒ \log_{2}\dfrac{\left({t}^{2} + 13\right)}{\left(\dfrac{5t}{2} + 1\right)} = 2

⇒(t2+13)(5t2+1)=22⇒ \dfrac{\left({t}^{2} + 13\right)}{\left(\dfrac{5t}{2} + 1\right)} = {2}^{2}

⇒t2+13=10t+4⇒ {t}^{2} + 13 = 10t + 4

⇒t2−10t+9=0⇒ {t}^{2} - 10t + 9 = 0

⇒t=1or9⇒ t = 1\text{or}9

So,

32α−4=1or9{3}^{2\alpha - 4} = 1\text{or}9

⇒32α−4=30or32⇒ {3}^{2\alpha - 4} = {3}^{0}\text{or}{3}^{2}

⇒2α−4=0or2⇒ 2\alpha - 4 = 0or2

⇒α=2,3⇒ \alpha = 2, 3

Now,

x2−2(∑α∈sα)2x+∑a∈s(α+1)2β=0{x}^{2} - 2{\left(\mathop{∑}_{\alpha \in s}\alpha\right)}^{2}x + \mathop{∑}_{a \in s}{\left(\alpha + 1\right)}^{2}\beta = 0

⇒x2−2((2+3)2x)+(32+42)β=0⇒ {x}^{2} - 2\left({\left(2 + 3\right)}^{2}x\right) + \left({3}^{2} + {4}^{2}\right)\beta = 0

⇒x2−50x+25β=0⇒ {x}^{2} - 50x + 25\beta = 0

Now for real roots

D≥0D \ge 0

⇒502−4×25β≥0⇒ {50}^{2} - 4 \times 25\beta \ge 0

⇒50−2β≥0⇒ 50 - 2\beta \ge 0

⇒β≤25⇒ \beta \le 25

So, maximum value of β\beta is 2525.

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