Sunday, July 1, 2012

log (x^2+3) - log (2x-5) = 0

First, we'll impose the constraints of existence of
logarithms. Since x^2+3 is positive for any value of x, we'll set the only
contraint:


2x -
5>0


2x>5


x>5/2


We'll
add  log (2x-5) both sides:


log (x^2+3) = log
(2x-5)


Since the bases are matching, we'll use the one to
one property:


x^2 + 3 = 2x -
5


We'll subtract 2x - 5:


x^2 +
3 - 2x + 5 = 0


We'll combine like
terms:


x^2 - 2x + 8 = 0


We'll
apply the quadratic formula:


x1 = [-b+sqrt(b^2 -
4ac)]/2a


x1 = [2+sqrt(4 -
32)]/2


Since sqrt (-28) is impossible to be
calculated, the equation has no real solutions.

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