Tuesday, August 28, 2012

how to solve log v3 (x+3)+ log v3 (x-5)=2the "V" means it is a base

log3 ( x+ 3) + log3 ( x-5) =
2


First we will determine the
domain,


==> x+ 3 > 0   and x-5 >
0


==> x > -3   and   x >
5


==> x > 5 is the
domain.......(1)


We will use logarithm properties to solve
for x.


We know that log a + log b= = log
ab


==> log3 (x+3) + log 3 ( x-5) = log3 (x+3)*(x-5)
= 2


Now we will open the
brackets.


==> log3 ( x^2 - 2x - 15) =
2


Now we will rewrite using he exponent
form.


==>  x^2 -2x - 15 =
3^2


==> x^2 - 2x - 15 =
9


==> x^2 - 2x - 24 =
0


Now we will
factor.


==> (x -6)(x+4) =
0


==> x = 6 > 5  ( belongs to the
domain)


==> x = -4  < 5 ( does NOT belong to
the domain)


Then the only solution is x =
6.

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