Friday, April 18, 2014

Solve for x : x^(1+log 2 sqrtx) = 16

This is a logarithmic
equation.


We'll take logarithms both side of the equation
and the logarithms will have the base 2:


log 2 [x^(1+log 2
sqrtx)] = log 2 16


We'll use the power property of
logarithms and we'll write 16 = 2^4:


(1+log 2 sqrtx) * log
2 x= log 2 2^4


[1+log 2 (x)^1/2] * log 2 x= 4*log 2
2


{1 + [log 2 (x)]/2}* log 2 x=
4


We'll remove the brackets form the left
side:


log 2 x + [(log 2 x)^2]/2 - 4 =
0


2*log 2 x + (log 2 x)^2 - 4 =
0


We'll substitute log 2 x =
t


t^2 + 2t - 4 = 0


We'll apply
the quadratic formula:


t1 =
[-2+sqrt(4+16)]/2


t1 =
(-2+2sqrt5)/2


t1 = -1+sqrt5


t2
= -1-sqrt5


 log 2 x =
t1


x1 =
2^-1+sqrt5


x2 =
2^-(1+sqrt5)


x2 =
1/2^(1+sqrt5)

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