Saturday, July 26, 2014

ln(-x)=ln(x^2-6)How to find out the value of x in the above problem..please help

Since the bases are matching, we'll apply one to one rule
of logarithms:


-x = x^2 -
6


We'll use the symmetrical property and we'll
have:


x^2 - 6 = -x


We'll shift
-x to the left:


x^2 + x - 6 =
0


We'll apply quadratic
formula:


x1 =
[-1+sqrt(1+24)]/2


x1 =
(-1+5)/2


x1 = -2


x2 =
-3


Now, we'll impose the constraints of existence of
logarithms:


x < 0


x^2 -
6 > 0


The expression is positive if x belongs to the
intervals: (-infinite;-sqrt6)U(+sqrt6 ; +infinite)


The
common interval of admissible values for x is
(-infinite;-sqrt6).


Since x = -2 doesn't
belong to this interval, the only solution of the equation is x =
-3.

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