Sunday, June 23, 2013

Solve for x x^(lnx/ln2)=6-8/x^(lnx/ln2)

We'll substitute x^(ln x/ln 2) by t and we'll re-write the
equation in t:


t  = 6 -
8/t


We'll multiply by t both
sides:


t^2 = 6t - 8


We'll move
all terms to one side:


t^2 - 6t + 8 =
0


Since the sum is 6 and the product is 8, we'll conclude
that the roots of the quadratic are:


t1 = 2 and t2 =
4


x^(ln x/ln 2) = t1


x^(ln
x/ln 2) = 2


But ln x/ln 2 = log 2
x


We'll take logarithms both
sides:


log2 (x^log2 x) = log2
2


We'll apply the power rule of
logarithms:


log2 (x^log2 x) =
1


(log2 x)^2 - 1 = 0


We'll
re-write the differnce of squares:


(log2 x - 1)(log2 x + 1)
= 0


log2 x - 1 = 0 => log2 x=1 => x =
2^1


x = 2


log2 x + 1 = 0
=> log2 x = -1 => x = 2^-1


x =
1/2


x^(ln x/ln 2) = t2


x^(ln
x/ln 2) = 4


log2 (x^log2 x) = log2
4


log2 (x^log2 x) = log2
2^2


log2 (x^log2 x) = 2log2
2


log2 (x^log2 x) = 2


log2
(x^log2 x) - 2 = 0


(log2 x)^2 - 2 =
0


(log2 x - sqrt2)(log2 x + sqrt2) =
0


log2 x - sqrt2 = 0


log2 x =
sqrt2 => x = 2^sqrt2


log2 x =- sqrt2 => x =
2^-sqrt2


All values of x that verify the
equation are: {1/2 ; 2 ; 2^sqrt2 ; 2^-sqrt2}.

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