The problem is to evaluate the expression $6 + \log_{\frac{3}{2}} \left\{ \frac{1}{3\sqrt{2}} \sqrt{4 - \frac{1}{3\sqrt{2}} \sqrt{4 - \frac{1}{3\sqrt{2}} \sqrt{4 - \frac{1}{3\sqrt{2}} \cdots }}} \right\}$.

AlgebraLogarithmsQuadratic EquationsRadicalsAlgebraic Manipulation
2025/4/22

1. Problem Description

The problem is to evaluate the expression 6+log32{132413241324132}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\}.

2. Solution Steps

Let x=413241324132x = \sqrt{4 - \frac{1}{3\sqrt{2}} \sqrt{4 - \frac{1}{3\sqrt{2}} \sqrt{4 - \frac{1}{3\sqrt{2}} \cdots }}}
Then x=4132xx = \sqrt{4 - \frac{1}{3\sqrt{2}} x}.
Squaring both sides, we get x2=4132xx^2 = 4 - \frac{1}{3\sqrt{2}} x.
Rearranging the terms, we have x2+132x4=0x^2 + \frac{1}{3\sqrt{2}} x - 4 = 0.
Multiplying by 323\sqrt{2}, we get 32x2+x122=03\sqrt{2} x^2 + x - 12\sqrt{2} = 0.
Using the quadratic formula, we have
x=1±124(32)(122)2(32)=1±1+4(3)(12)(2)62=1±1+28862=1±28962=1±1762x = \frac{-1 \pm \sqrt{1^2 - 4(3\sqrt{2})(-12\sqrt{2})}}{2(3\sqrt{2})} = \frac{-1 \pm \sqrt{1 + 4(3)(12)(2)}}{6\sqrt{2}} = \frac{-1 \pm \sqrt{1 + 288}}{6\sqrt{2}} = \frac{-1 \pm \sqrt{289}}{6\sqrt{2}} = \frac{-1 \pm 17}{6\sqrt{2}}.
Since xx must be positive, we take the positive root, so x=1+1762=1662=832x = \frac{-1 + 17}{6\sqrt{2}} = \frac{16}{6\sqrt{2}} = \frac{8}{3\sqrt{2}}.
Then the expression inside the logarithm is 132832=89(2)=818=49\frac{1}{3\sqrt{2}} \cdot \frac{8}{3\sqrt{2}} = \frac{8}{9(2)} = \frac{8}{18} = \frac{4}{9}.
Now we have 6+log32(49)=6+log32((23)2)=6+2log32(23)=6+2log32((32)1)=6+2(1)log32(32)=62(1)=62=46 + \log_{\frac{3}{2}} \left( \frac{4}{9} \right) = 6 + \log_{\frac{3}{2}} \left( \left( \frac{2}{3} \right)^2 \right) = 6 + 2 \log_{\frac{3}{2}} \left( \frac{2}{3} \right) = 6 + 2 \log_{\frac{3}{2}} \left( \left( \frac{3}{2} \right)^{-1} \right) = 6 + 2(-1) \log_{\frac{3}{2}} \left( \frac{3}{2} \right) = 6 - 2(1) = 6 - 2 = 4.

3. Final Answer

4

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