Precalculus Examples

$\log_{x} (256) = - 4$

Step 1

Add $4$ to both sides of the equation.

$\log_{x} (256) + 4 = 0$

Step 2

Subtract $4$ from both sides of the equation.

$\log_{x} (256) = - 4$

Step 3

Rewrite $\log_{x} (256) = - 4$ 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 $b^{y} = x$ .

$x^{- 4} = 256$

Step 4

Solve for $x$ .

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Step 4.1

Rewrite the expression using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$\frac{1}{x^{4}} = 256$

Step 4.2

Find the LCD of the terms in the equation.

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Step 4.2.1

Finding the LCD of a list of values is the same as finding the LCM of the denominators of those values.

$x^{4}, 1$

Step 4.2.2

The LCM of one and any expression is the expression.

$x^{4}$

Step 4.3

Multiply each term in $\frac{1}{x^{4}} = 256$ by $x^{4}$ to eliminate the fractions.

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Step 4.3.1

Multiply each term in $\frac{1}{x^{4}} = 256$ by $x^{4}$ .

$\frac{1}{x^{4}} x^{4} = 256 x^{4}$

Step 4.3.2

Simplify the left side.

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Step 4.3.2.1

Cancel the common factor of $x^{4}$ .

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Step 4.3.2.1.1

Cancel the common factor.

$\frac{1}{x^{4}} x^{4} = 256 x^{4}$

Step 4.3.2.1.2

Rewrite the expression.

$1 = 256 x^{4}$

Step 4.4

Solve the equation.

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Step 4.4.1

Rewrite the equation as $256 x^{4} = 1$ .

$256 x^{4} = 1$

Step 4.4.2

Divide each term in $256 x^{4} = 1$ by $256$ and simplify.

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Step 4.4.2.1

Divide each term in $256 x^{4} = 1$ by $256$ .

$\frac{256 x^{4}}{256} = \frac{1}{256}$

Step 4.4.2.2

Simplify the left side.

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Step 4.4.2.2.1

Cancel the common factor of $256$ .

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Step 4.4.2.2.1.1

Cancel the common factor.

$\frac{256 x^{4}}{256} = \frac{1}{256}$

Step 4.4.2.2.1.2

Divide $x^{4}$ by $1$ .

$x^{4} = \frac{1}{256}$

Step 4.4.3

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x = \pm \sqrt[4]{\frac{1}{256}}$

Step 4.4.4

Simplify $\pm \sqrt[4]{\frac{1}{256}}$ .

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Step 4.4.4.1

Rewrite $\sqrt[4]{\frac{1}{256}}$ as $\frac{\sqrt[4]{1}}{\sqrt[4]{256}}$ .

$x = \pm \frac{\sqrt[4]{1}}{\sqrt[4]{256}}$

Step 4.4.4.2

Any root of $1$ is $1$ .

$x = \pm \frac{1}{\sqrt[4]{256}}$

Step 4.4.4.3

Simplify the denominator.

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Step 4.4.4.3.1

Rewrite $256$ as $4^{4}$ .

$x = \pm \frac{1}{\sqrt[4]{4^{4}}}$

Step 4.4.4.3.2

Pull terms out from under the radical, assuming positive real numbers.

$x = \pm \frac{1}{4}$

Step 4.4.5

The complete solution is the result of both the positive and negative portions of the solution.

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Step 4.4.5.1

First, use the positive value of the $\pm$ to find the first solution.

$x = \frac{1}{4}$

Step 4.4.5.2

Next, use the negative value of the $\pm$ to find the second solution.

$x = - \frac{1}{4}$

Step 4.4.5.3

The complete solution is the result of both the positive and negative portions of the solution.

$x = \frac{1}{4}, - \frac{1}{4}$

Step 5

Exclude the solutions that do not make $\log_{x} (256) + 4 = 0$ true.

$x = \frac{1}{4}$