Question

Solve the equation log(5x)-log(x-3)=1​

Answer 1

Answer:

x =6

Step-by-step explanation:

log(5x) - log(x - 3) = 1

Recall that  the logarithm of a fraction is the difference of the logarithms,

so, the difference between two logarithms is logarithm  of the fraction. Then,

$\begin{array}{rcll}\\\\\log \dfrac{5x}{x-3} & = & 1 &\\\\\dfrac{5x}{x - 3} & = & 10 & \text{Took the antilogarithm of each side}\\\\5x & = & 10(x - 3) & \text{Multiplied each side by x - 3}\\5x & = & 10x - 30 & \text{Distributed the 10}\\-5x & = & -30 & \text{Subtracted 10 x from each side}\\x & = & \mathbf{6} & \text{Divided each side by -5}\\\end{array}$

Check:

$\begin{array}{rcl}\log(5\times6) - \log (6 - 3) & = & 1\\\log 30 - \log 3 & = &1\\\\\log \dfrac{30}{3} & = & 1\\\\\log 10 & = & 1\\1 & = & 1\\\end{array}$

OK.

Answer 2

Answer:

x = 6

Step-by-step explanation:

Using the rules of logarithms

• log x - log y ⇔ log ($\frac{x}{y}$ )

• $log_{b}$ x = n ⇔ x = $b^{n}$

Given

log(5x) - log(x - 3) = 1

log ( $\frac{5x}{x-3}$ ) = 1, then

$\frac{5x}{x-3}$ = $10^{1}$ = 10 ( cross- multiply )

10(x - 3) = 5x

10x - 30 = 5x ( subtract 5x from both sides )

5x - 30 = 0 ( add 30 to both sides )

5x = 30 ( divide both sides by 5 )

x = 6