Given that
lo g 2 ( lo g 8 x ) = lo g 8 ( lo g 2 x ) ,
find the value of ( lo g 2 x ) 2 .
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lo g 2 ( lo g 8 x ) = lo g 8 ( lo g 2 x )
⟹ lo g 2 ( 3 lo g 2 x ) = 3 lo g 2 ( lo g 2 x )
⟹ lo g 2 ( 3 lo g 2 x ) = lo g 2 ( ( lo g 2 x ) 1 / 3 )
⟹ 3 lo g 2 x = ( lo g 2 x ) 1 / 3
⟹ 2 7 ( lo g 2 x ) 3 = lo g 2 x
⟹ ( lo g 2 x ) 2 = 2 7 .
I understand your method right down to the second last line . From there you are multiplying the RHS by 27 and, after that, diving both sides by Log x to base 2 (?)
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Cross multiplication. lo g 2 x ( lo g 2 x ) 3 = 2 7
l o g 2 ( 3 1 l o g 2 x ) = 3 1 l o g 2 ( l o g 2 x )
3 l o g 2 3 1 + 3 l o g 2 ( l o g 2 x ) = l o g 2 ( l o g 2 x )
2 l o g 2 ( l o g 2 x ) = l o g 2 2 7
l o g 2 x 2 = 2 l o g 2 2 7
l o g 2 x 2 = 2 7
I can see why some find this somewhat tricky at first.
log((1/3) log(x)) = 1/3 log(log(x))
(1/3)*log(x) = (log(x))^(1/3)
(log(x))^3 = 27 (log(x))
(log(x))^2 = 27
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Using the Properties of Logarithms , this equation can be written as
lo g 2 ( ( 3 1 ) lo g 2 x ) = ( 3 1 ) lo g 2 ( lo g 2 x )
⟹ ( 3 1 ) lo g 2 x = ( lo g 2 x ) 3 1
⟹ ( lo g 2 x ) 3 2 = 3 ⟹ lo g 2 x = 3 3 ,
the square of which is 9 ⋅ 3 = 2 7 .