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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