Solve the logarithmic equation $2\log \left(x\right)-\log \left(x+6\right)=0$

Step-by-step Solution

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Final answer to the problem

$x=3$
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Step-by-step Solution

How should I solve this problem?

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1

Apply the formula: $a\log_{b}\left(x\right)$$=\log_{b}\left(x^a\right)$

$\log \left(x^2\right)-\log \left(x+6\right)=0$
2

The difference of two logarithms of equal base $b$ is equal to the logarithm of the quotient: $\log_b(x)-\log_b(y)=\log_b\left(\frac{x}{y}\right)$

$\log \left(\frac{x^2}{x+6}\right)=0$

Rewrite the number $0$ as a logarithm of base $10$

$\log \left(\frac{x^2}{x+6}\right)=\log \left(10^0\right)$

Any expression (except $0$ and $\infty$) to the power of $0$ is equal to $1$

$\log \left(\frac{x^2}{x+6}\right)=\log \left(1\right)$
3

Rewrite the number $0$ as a logarithm of base $10$

$\log \left(\frac{x^2}{x+6}\right)=\log \left(1\right)$
4

For two logarithms of the same base to be equal, their arguments must be equal. In other words, if $\log(a)=\log(b)$ then $a$ must equal $b$

$\frac{x^2}{x+6}=1$

Multiply both sides of the equation by $x+6$

$x^2=1\left(x+6\right)$

Any expression multiplied by $1$ is equal to itself

$x^2=x+6$
5

Multiply both sides of the equation by $x+6$

$x^2=x+6$
6

Move everything to the left hand side of the equation

$x^2-x-6=0$
7

Factor the trinomial $x^2-x-6$ finding two numbers that multiply to form $-6$ and added form $-1$

$\begin{matrix}\left(2\right)\left(-3\right)=-6\\ \left(2\right)+\left(-3\right)=-1\end{matrix}$
8

Rewrite the polynomial as the product of two binomials consisting of the sum of the variable and the found values

$\left(x+2\right)\left(x-3\right)=0$
9

Break the equation in $2$ factors and set each factor equal to zero, to obtain simpler equations

$x+2=0,\:x-3=0$
10

Solve the equation ($1$)

$x+2=0$
11

We need to isolate the dependent variable $x$, we can do that by simultaneously subtracting $2$ from both sides of the equation

$x+2-2=0-2$
12

Canceling terms on both sides

$x=-2$
13

Solve the equation ($2$)

$x-3=0$
14

We need to isolate the dependent variable $x$, we can do that by simultaneously subtracting $-3$ from both sides of the equation

$x-3+3=0+3$
15

Canceling terms on both sides

$x=3$
16

Combining all solutions, the $2$ solutions of the equation are

$x=-2,\:x=3$

Verify that the solutions obtained are valid in the initial equation

17

The valid solutions to the logarithmic equation are the ones that, when replaced in the original equation, don't result in any logarithm of negative numbers or zero, since in those cases the logarithm does not exist

$x=3$

Final answer to the problem

$x=3$

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Function Plot

Plotting: $2\log \left(x\right)-\log \left(x+6\right)$

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0
a
b
c
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f
g
m
n
u
v
w
x
y
z
.
(◻)
+
-
×
◻/◻
/
÷
2

e
π
ln
log
log
lim
d/dx
Dx
|◻|
θ
=
>
<
>=
<=
sin
cos
tan
cot
sec
csc

asin
acos
atan
acot
asec
acsc

sinh
cosh
tanh
coth
sech
csch

asinh
acosh
atanh
acoth
asech
acsch

How to improve your answer:

Main Topic: Logarithmic Equations

Are those equations in which the unknown variable appears within a logarithm.

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