Thursday, November 3, 2011

Solve for x: log (x+5) = 2 - log (2x)

log (x+5) = 2- log (2x).


I
believe that you need to determine the values of x that satisfies the
equation.


We will use logarithm properties to solve for
x.


First we will add log 2x to both
sides.


==> log (x+ 5) + log (2x) =
2


Now we know that log a + log b= log
a*b.


==> log (x+5)*2x =
2


==> log ( 2x^2 +10x) =
2


Now we will rewrite into the exponent
form.


==> 2x^2 + 10x =
10^2


==> 2x^2 + 10x =
100


==> 2x^2 + 10 x -100 =
0


Now we will divide by
2.


==> x^2 + 5x -50 =
0


Now we will
factor.


==> (x+10) (x-5) =
0


==> x1= -10 ==> Not valid because log ca
not be negative.)


==> x2=
5


Let us check .


==>
log (5+5) = 2 - log 2*5


==> log 10 = 2- log
10


==> 1 =
2-1


==> 1 = 1


Then the
answer is valid


==> Then the answer is
x= 5.

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