Calculus Examples

$f (x) = \frac{1}{x} + \ln (x)$

Step 1

Find the first derivative.

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Step 1.1

Find the first derivative.

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Step 1.1.1

By the Sum Rule, the derivative of $\frac{1}{x} + \ln (x)$ with respect to $x$ is $\frac{d}{d x} [\frac{1}{x}] + \frac{d}{d x} [\ln (x)]$ .

$\frac{d}{d x} [\frac{1}{x}] + \frac{d}{d x} [\ln (x)]$

Step 1.1.2

Evaluate $\frac{d}{d x} [\frac{1}{x}]$ .

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Step 1.1.2.1

Rewrite $\frac{1}{x}$ as $x^{- 1}$ .

$\frac{d}{d x} [x^{- 1}] + \frac{d}{d x} [\ln (x)]$

Step 1.1.2.2

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = - 1$ .

$- x^{- 2} + \frac{d}{d x} [\ln (x)]$

Step 1.1.3

The derivative of $\ln (x)$ with respect to $x$ is $\frac{1}{x}$ .

$- x^{- 2} + \frac{1}{x}$

Step 1.1.4

Simplify.

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Step 1.1.4.1

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

$- \frac{1}{x^{2}} + \frac{1}{x}$

Step 1.1.4.2

Reorder terms.

$f' (x) = \frac{1}{x} - \frac{1}{x^{2}}$

Step 1.2

The first derivative of $f (x)$ with respect to $x$ is $\frac{1}{x} - \frac{1}{x^{2}}$ .

$\frac{1}{x} - \frac{1}{x^{2}}$

Step 2

Set the first derivative equal to $0$ then solve the equation $\frac{1}{x} - \frac{1}{x^{2}} = 0$ .

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Step 2.1

Set the first derivative equal to $0$ .

$\frac{1}{x} - \frac{1}{x^{2}} = 0$

Step 2.2

Find the LCD of the terms in the equation.

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Step 2.2.1

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

$x, x^{2}, 1$

Step 2.2.2

Since $x, x^{2}, 1$ contains both numbers and variables, there are two steps to find the LCM. Find LCM for the numeric part $1, 1, 1$ then find LCM for the variable part $x^{1}, x^{2}$ .

Step 2.2.3

The LCM is the smallest positive number that all of the numbers divide into evenly.

1. List the prime factors of each number.

2. Multiply each factor the greatest number of times it occurs in either number.

Step 2.2.4

The number $1$ is not a prime number because it only has one positive factor, which is itself.

Not prime

Step 2.2.5

The LCM of $1, 1, 1$ is the result of multiplying all prime factors the greatest number of times they occur in either number.

$1$

Step 2.2.6

The factor for $x^{1}$ is $x$ itself.

$x^{1} = x$

$x$ occurs $1$ time.

Step 2.2.7

The factors for $x^{2}$ are $x \cdot x$ , which is $x$ multiplied by each other $2$ times.

$x^{2} = x \cdot x$

$x$ occurs $2$ times.

Step 2.2.8

The LCM of $x^{1}, x^{2}$ is the result of multiplying all prime factors the greatest number of times they occur in either term.

$x \cdot x$

Step 2.2.9

Multiply $x$ by $x$ .

$x^{2}$

Step 2.3

Multiply each term in $\frac{1}{x} - \frac{1}{x^{2}} = 0$ by $x^{2}$ to eliminate the fractions.

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Step 2.3.1

Multiply each term in $\frac{1}{x} - \frac{1}{x^{2}} = 0$ by $x^{2}$ .

$\frac{1}{x} x^{2} - \frac{1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2

Simplify the left side.

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Step 2.3.2.1

Simplify each term.

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Step 2.3.2.1.1

Cancel the common factor of $x$ .

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Step 2.3.2.1.1.1

Factor $x$ out of $x^{2}$ .

$\frac{1}{x} (x \cdot x) - \frac{1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2.1.1.2

Cancel the common factor.

$\frac{1}{x} (x \cdot x) - \frac{1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2.1.1.3

Rewrite the expression.

$x - \frac{1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2.1.2

Cancel the common factor of $x^{2}$ .

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Step 2.3.2.1.2.1

Move the leading negative in $- \frac{1}{x^{2}}$ into the numerator.

$x + \frac{- 1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2.1.2.2

Cancel the common factor.

$x + \frac{- 1}{x^{2}} x^{2} = 0 x^{2}$

Step 2.3.2.1.2.3

Rewrite the expression.

$x - 1 = 0 x^{2}$

Step 2.3.3

Simplify the right side.

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Step 2.3.3.1

Multiply $0$ by $x^{2}$ .

$x - 1 = 0$

Step 2.4

Add $1$ to both sides of the equation.

$x = 1$

Step 3

Find the values where the derivative is undefined.

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Step 3.1

Set the denominator in $\frac{1}{x}$ equal to $0$ to find where the expression is undefined.

$x = 0$

Step 3.2

Set the denominator in $\frac{1}{x^{2}}$ equal to $0$ to find where the expression is undefined.

$x^{2} = 0$

Step 3.3

Solve for $x$ .

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Step 3.3.1

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

$x = \pm \sqrt{0}$

Step 3.3.2

Simplify $\pm \sqrt{0}$ .

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Step 3.3.2.1

Rewrite $0$ as $0^{2}$ .

$x = \pm \sqrt{0^{2}}$

Step 3.3.2.2

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

$x = \pm 0$

Step 3.3.2.3

Plus or minus $0$ is $0$ .

$x = 0$

Step 4

Evaluate $\frac{1}{x} + \ln (x)$ at each $x$ value where the derivative is $0$ or undefined.

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Step 4.1

Evaluate at $x = 1$ .

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Step 4.1.1

Substitute $1$ for $x$ .

$\frac{1}{1} + \ln (1)$

Step 4.1.2

Simplify.

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Step 4.1.2.1

Simplify each term.

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Step 4.1.2.1.1

Divide $1$ by $1$ .

$1 + \ln (1)$

Step 4.1.2.1.2

The natural logarithm of $1$ is $0$ .

$1 + 0$

Step 4.1.2.2

Add $1$ and $0$ .

$1$

Step 4.2

Evaluate at $x = 0$ .

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Step 4.2.1

Substitute $0$ for $x$ .

$\frac{1}{0} + \ln (0)$

Step 4.2.2

The natural logarithm of zero is undefined.

Undefined

Step 4.3

List all of the points.

$(1, 1)$

Step 5