Precalculus Examples

$y = \log_{2} (x - 4)$

Step 1

Find the asymptotes.

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Step 1.1

Set the argument of the logarithm equal to zero.

$x - 4 = 0$

Step 1.2

Add $4$ to both sides of the equation.

$x = 4$

Step 1.3

The vertical asymptote occurs at $x = 4$ .

Vertical Asymptote: $x = 4$

Step 2

Find the point at $x = 5$ .

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Step 2.1

Replace the variable $x$ with $5$ in the expression.

$f (5) = \log_{2} ((5) - 4)$

Step 2.2

Simplify the result.

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Step 2.2.1

Subtract $4$ from $5$ .

$f (5) = \log_{2} (1)$

Step 2.2.2

Logarithm base $2$ of $1$ is $0$ .

$f (5) = 0$

Step 2.2.3

The final answer is $0$ .

$0$

Step 2.3

Convert $0$ to decimal.

$y = 0$

Step 3

Find the point at $x = 6$ .

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Step 3.1

Replace the variable $x$ with $6$ in the expression.

$f (6) = \log_{2} ((6) - 4)$

Step 3.2

Simplify the result.

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Step 3.2.1

Subtract $4$ from $6$ .

$f (6) = \log_{2} (2)$

Step 3.2.2

Logarithm base $2$ of $2$ is $1$ .

$f (6) = 1$

Step 3.2.3

The final answer is $1$ .

$1$

Step 3.3

Convert $1$ to decimal.

$y = 1$

Step 4

Find the point at $x = 8$ .

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Step 4.1

Replace the variable $x$ with $8$ in the expression.

$f (8) = \log_{2} ((8) - 4)$

Step 4.2

Simplify the result.

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Step 4.2.1

Subtract $4$ from $8$ .

$f (8) = \log_{2} (4)$

Step 4.2.2

Logarithm base $2$ of $4$ is $2$ .

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Step 4.2.2.1

Rewrite as an equation.

$\log_{2} (4) = x$

Step 4.2.2.2

Rewrite $\log_{2} (4) = x$ in exponential form using the definition of a logarithm. If $x$ and $b$ are positive real numbers and $b$ does not equal $1$ , then $\log_{b} (x) = y$ is equivalent to $b^{y} = x$ .

$2^{x} = 4$

Step 4.2.2.3

Create equivalent expressions in the equation that all have equal bases.

$2^{x} = 2^{2}$

Step 4.2.2.4

Since the bases are the same, the two expressions are only equal if the exponents are also equal.

$x = 2$

Step 4.2.2.5

The variable $x$ is equal to $2$ .

$f (8) = 2$

Step 4.2.3

The final answer is $2$ .

$2$

Step 4.3

Convert $2$ to decimal.

$y = 2$

Step 5

The log function can be graphed using the vertical asymptote at $x = 4$ and the points $(5, 0), (6, 1), (8, 2)$ .

Vertical Asymptote: $x = 4$

$\begin{array}{c} x & y \\ 5 & 0 \\ 6 & 1 \\ 8 & 2 \end{array}$

Step 6