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JEE Advanced · Mathematics · 2. Quadratic Equations

The value of
\(6+\log _{\frac{3}{2}}\)\(\left(\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}}} \cdots}}\right)\) is

  1. A 1
  2. B 2
  3. C 3
  4. D 4
Verified Solution

Answer & Solution

Correct Answer

(D) 4

Step-by-step Solution

Detailed explanation

Let \(x=\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}} \sqrt{4-\frac{1}{3 \sqrt{2}}}}} \ldots \ldots\)
\(\Rightarrow x=\frac{1}{3 \sqrt{2}} \sqrt{4-x}\)
\(\Rightarrow 3 \sqrt{2} x=\sqrt{4-x}\)
\(\Rightarrow 18 x^{2}=4-x \)
\(\Rightarrow 18 x^{2}+x-4=0 \)
\(\Rightarrow (9 x-4)(2 x+1)=0 \)
\(\Rightarrow x=\frac{4}{9} \text { or } x=-\frac{1}{2}\)
(Not possible because log is not define for -ve value)
\(\therefore 6+\log _{\frac{3}{2}}\left(\frac{4}{9}\right)=6+\log _{\frac{3}{2}}\left(\frac{3}{2}\right)^{-2}\)
\(=6-2=4\)
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