Precalculus Examples

$\ln (8 x) = 4.2$

Step 1

To solve for $x$ , rewrite the equation using properties of logarithms.

$e^{\ln (8 x)} = e^{4.2}$

Step 2

Rewrite $\ln (8 x) = 4.2$ in exponential form using the definition of a logarithm. If $x$ and $b$ are positive real numbers and $b \neq 1$ , then $\log_{b} (x) = y$ is equivalent to $b^{y} = x$ .

$e^{4.2} = 8 x$

Step 3

Solve for $x$ .

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Step 3.1

Rewrite the equation as $8 x = e^{4.2}$ .

$8 x = e^{4.2}$

Step 3.2

Divide each term in $8 x = e^{4.2}$ by $8$ and simplify.

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Step 3.2.1

Divide each term in $8 x = e^{4.2}$ by $8$ .

$\frac{8 x}{8} = \frac{e^{4.2}}{8}$

Step 3.2.2

Simplify the left side.

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Step 3.2.2.1

Cancel the common factor of $8$ .

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Step 3.2.2.1.1

Cancel the common factor.

$\frac{8 x}{8} = \frac{e^{4.2}}{8}$

Step 3.2.2.1.2

Divide $x$ by $1$ .

$x = \frac{e^{4.2}}{8}$

Step 4

The result can be shown in multiple forms.

Exact Form:

$x = \frac{e^{4.2}}{8}$

Decimal Form:

$x = 8.33579138 \dots$