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JEE Main 20264 AprilEvening Shift
Exam
JEE Main
Year
2026
Date
4 April
Shift
Evening Shift
Subject
Mathematics
Chapter
Sequences and Series

JEE Main 2026 · 4 April · Evening Shift · Mathematics · Sequences and Series

Let α=(1)/(4)+(1)/(8)+(1)/(16)+ ∞ and β=(1)/(3)+(1)/(9)+(1)/(27)+ ∞...

Let α=14+18+116+…∞\alpha=\dfrac{1}{4}+\dfrac{1}{8}+\dfrac{1}{16}+\ldots\infty and β=13+19+127+…∞\beta=\dfrac{1}{3}+\dfrac{1}{9}+\dfrac{1}{27}+\ldots\infty. Then the value of (0.2)log⁡5(α)+(0.04)log⁡5(β)(0.2)^{\log_{\sqrt{5}}(\alpha)}+(0.04)^{\log_5(\beta)} is equal to:

Options

  1. A44
  2. B55
  3. C88
  4. D2525

Correct answer

C. 88

Step-by-step solution

The sum of an infinite geometric progression is given by S∞=a1−rS_{\infty} = \dfrac{a}{1-r}.

For α\alpha, a=14a = \dfrac{1}{4} and r=12r = \dfrac{1}{2}:
α=141−12=12\alpha = \dfrac{\dfrac{1}{4}}{1 - \dfrac{1}{2}} = \dfrac{1}{2}

For β\beta, a=13a = \dfrac{1}{3} and r=13r = \dfrac{1}{3}:
β=131−13=12\beta = \dfrac{\dfrac{1}{3}}{1 - \dfrac{1}{3}} = \dfrac{1}{2}

Now, evaluating the first term:
(0.2)log⁡5(α)=(5−1)log⁡51/2(1/2)(0.2)^{\log_{\sqrt{5}}(\alpha)} = \left(5^{-1}\right)^{\log_{5^{1/2}}(1/2)}
Using the property log⁡ak(x)=1klog⁡a(x)\log_{a^k}(x) = \dfrac{1}{k}\log_a(x):
log⁡51/2(1/2)=2log⁡5(1/2)=log⁡5(1/4)\log_{5^{1/2}}(1/2) = 2\log_5(1/2) = \log_5(1/4)
Thus, \left(5^{-1}\right)^{\log_5(1/4)} = 5^{-\log_5(1/4)} = 5^{\log_5(4)} = 4<br><br>Evaluatingthesecondterm:<br><br><br>Evaluating the second term:<br>(0.04)^{\log_5(\beta)} = \left(5^{-2}\right)^{\log_5(1/2)}<br>(5−2)log⁡5(1/2)=5−2log⁡5(1/2)=5log⁡5(4)=4<br>\left(5^{-2}\right)^{\log_5(1/2)} = 5^{-2\log_5(1/2)} = 5^{\log_5(4)} = 4

Adding both terms:
(0.2)log⁡5(α)+(0.04)log⁡5(β)=4+4=8(0.2)^{\log_{\sqrt{5}}(\alpha)} + (0.04)^{\log_5(\beta)} = 4 + 4 = 8

Answer: 88
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