First, we'll impose the constraints of existence of
logarithms:
x>0 and x different from
1
2x>0 and x different from
1/2
4x > 0 and x different from
1/4
Now, we'll solve the equation interchanging the bases
and arguments at each of the terms of the given
equation.
1/log2 x + 1/log2 2x = 1/log2
4x
We'll apply the product property of
logarithms:
log2 2x = log2 2 + log2
x
But log2 2 = 1
log2 2x = 1 +
log2 x
log2 4x = log2 4 + log2
x
log2 4x = log2 2^2 + log2
x
log2 4x = 2log2 2 + log2
x
log2 4x = 2 + log2 x
We'll
re-write the equation:
1/log2 x + 1/(1 + log2 x) = 1/(2 +
log2 x)
We notice the presence of log2 x all over the
equation, so, we'll substitute it by t.
1/t + 1/(1+t) =
1/(2+t)
We'll multiply each terms by
t(1+t)(2+t):
t(1+t)(2+t)/t + t(1+t)(2+t)/(1+t) =
t(1+t)(2+t)/(2+t)
We'll simplify and we'll
get:
(1+t)(2+t) + t(2+t) =
t(1+t)
We'll remove the brackets using
FOIL:
2 + 3t + t^2 + 2t + t^2 = t +
t^2
We'll subtract t + t^2:
2
+ 3t + t^2 + 2t + t^2 - t - t^2 = 0
We'll combine like
terms:
t^2 + 4t + 2 = 0
We'll
apply quadratic formula:
t1 = [-4+sqrt(16 -
8)]/2
t1 = -2+sqrt2
t2 =
-2-sqrt2
But log2 x = t
log2 x
= -2+sqrt2
x1 =
2^(-2+sqrt2)
x2 =
1/2^(2+sqrt2)
The solutions of the equation
are: x1 = 2^(-2+sqrt2) and x2 = 1/2^(2+sqrt2).
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