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Bunuel
If \(\sqrt{\sqrt{\sqrt{5x}}} = \sqrt[6]{4x}\), what is the range of the possible values of x?


A. 0
B. 1/4
C. 125/256
D. 1/2
E. 131/256


(5x)^1/8 = (4x)^1/6

raising to 24 on both sides
(5x)^3= (4x)^4
125* x^3 = 256* x^4
x= 125/256
IMO C
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\(((4x)^\frac{1}{6})^{2*2*2}\) = 5x

\(((4x)^\frac{4}{3})\) = 5x

\(((x)^\frac{4}{3})\) = \(\frac{{5x}}{4^{\frac{4}{3}}}\)

\(x^{\frac{1}{3}} = \frac{5}{4^{\frac{4}{3}}}\)

Cubing on both sides,

\(x = (\frac{5^3}{4^4})\)

x = 125/256

OPTION: C
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Hi,
There is just one value of x, i.e x=125/256, so range should be zero. How come range is 125/256 ?
pl. explain

Thanks in advance
Snigdha
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Bunuel
If \(\sqrt{\sqrt{\sqrt{5x}}} = \sqrt[6]{4x}\), what is the range of the possible values of x?

A. 0
B. 1/4
C. 125/256
D. 1/2
E. 131/256

note: x=0 is a possible value;

\(\sqrt{\sqrt{\sqrt{5x}}} = \sqrt[6]{4x}\)
\((5x)^{1/8} =(4x)^{1/6}\)
\((5x)=[(4x)^{1/6}]^8\)
\(5x=(4x)^{4/3}\)
\(5x=4^{4/3}x^{4/3}\)
\(5/4^{4/3}=x^{4/3}/x\)
\(5/4^{4/3}=x^{4/3-1}\)
\([5/4^{4/3}]^3=[x^{1/3}]^3\)
\(x=5^3/4^4=125/256\)

range: 125/256-0=125/256

Ans (C)
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Snigdha241
Hi,
There is just one value of x, i.e x=125/256, so range should be zero. How come range is 125/256 ?
pl. explain

Thanks in advance
Snigdha


While solving the problem we arrive at a position:

5^6 * x^6 = 4^8 *x^8

And we go ahead and cancel the X^6 ( we can only do so if x is not 0 ).

if x=0, the equation will be satisfied. hence 0 is also a solution. and the other is 125/256.

Range = 125/256 -0

Hope this helps!!
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Does taking LCM not change the solution that needs to be derived from this??
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Ayushi0002

Bunuel
Official Solution:

If \(\sqrt{\sqrt{\sqrt{5x}}} = \sqrt[6]{4x}\), what is the range of the possible values of \(x\)?

A. \(0\)
B. \(\frac{1}{4}\)
C. \(\frac{125}{256}\)
D. \(\frac{1}{2}\)
E. \(\frac{131}{256}\)


\(\sqrt{\sqrt{\sqrt{5x}}} = \sqrt[6]{4x}\);

\((5x)^{\frac{1}{2}*\frac{1}{2}*\frac{1}{2}} =(4x)^{\frac{1}{6}}\);

\((5x)^{\frac{1}{8}} =(4x)^{\frac{1}{6}}\);

Take to the power of 24 (the LCM of 8 and 6): \((5x)^3 =(4x)^4\);

\(x^3(256x-125)=0\);

\(x=0\) or \(x=\frac{125}{256}\).

The range of the possible values of \(x\) is therefore \(\frac{125}{256}-0=\frac{125}{256}\).


Answer: C

Does taking LCM not change the solution that needs to be derived from this??

We are taking the expression to the 24th power to simplify the equation, but we are still solving for the value of x. This step does not change the solution, it just helps eliminate fractional exponents.
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