Saturday, July 20, 2013

Solve for real x:log(5) (x+4) = log(5) (5x+5)

Before solving the equation, we'll impose conditions of
existence of the
logarithms.


x+4>0


x>-4


and


5(x+1)>0


x>-1


The
range of values admissible, for the equation to exist: (-1,
+inf).


We notice that the logarithms have matching bases,
so we can apply the one to one
property:


x+4=5x+5


We'll move
all terms to one
side:


x-5x+4-5=0


-4x -
1=0


We'll add 1 both
sides:


-4x = 1


x =
-1/4


x=-0.25


After finding the
value for x, we'll have to check if it is a solution for the equation, so, we'll have to
verify if it is belonging to the range of values (-1, +inf). We notice that -0.25 is
belonging to the interval (-1,
+inf).


x=-0.25

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