Monday, January 26, 2015

ln (x+2) - ln 3x = ln 5

We'll set the constraints of existence of
logarithms:


x+2>0


x>-2


3x>0


x>0


The
common interval of admissible values for x is
(0,+inf.).


Now,we'll could solve the equation in this way,
also:


We'll subtract ln (x+2) both
sides:


- ln 3x = ln 5 - ln
(x+2)


We'll multiply by -1 both
sides:


ln 3x = ln (x+2) - ln
5


We'll apply the quotient property of
logarithms:


ln 3x = ln
[(x+2)/5]


Because the bases of logarithms are matching,
we'll apply the one to one property:


3x =
(x+2)/5


We'll cross
multiply;


15x = x+2


We'll
subtract x both sides:


14x =
2


We'll divide by 14:


x =
2/14


x = 1/7>0


Since
the value for x is in the interval of admissible values, the solution is
valid.

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