Calculus Examples

$\arctan (\frac{9}{x}) + \arctan (\frac{3}{x})$

Step 1

By the Sum Rule, the derivative of $\arctan (\frac{9}{x}) + \arctan (\frac{3}{x})$ with respect to $x$ is $\frac{d}{d x} [\arctan (\frac{9}{x})] + \frac{d}{d x} [\arctan (\frac{3}{x})]$ .

$\frac{d}{d x} [\arctan (\frac{9}{x})] + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2

Evaluate $\frac{d}{d x} [\arctan (\frac{9}{x})]$ .

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Step 2.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \arctan (x)$ and $g (x) = \frac{9}{x}$ .

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Step 2.1.1

To apply the Chain Rule, set $u_{1}$ as $\frac{9}{x}$ .

$\frac{d}{d u_{1}} [\arctan (u_{1})] \frac{d}{d x} [\frac{9}{x}] + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.1.2

The derivative of $\arctan (u_{1})$ with respect to $u_{1}$ is $\frac{1}{1 + {u_{1}}^{2}}$ .

$\frac{1}{1 + {u_{1}}^{2}} \frac{d}{d x} [\frac{9}{x}] + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.1.3

Replace all occurrences of $u_{1}$ with $\frac{9}{x}$ .

$\frac{1}{1 + {(\frac{9}{x})}^{2}} \frac{d}{d x} [\frac{9}{x}] + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.2

Since $9$ is constant with respect to $x$ , the derivative of $\frac{9}{x}$ with respect to $x$ is $9 \frac{d}{d x} [\frac{1}{x}]$ .

$\frac{1}{1 + {(\frac{9}{x})}^{2}} (9 \frac{d}{d x} [\frac{1}{x}]) + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.3

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

$\frac{1}{1 + {(\frac{9}{x})}^{2}} (9 \frac{d}{d x} [x^{- 1}]) + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.4

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

$\frac{1}{1 + {(\frac{9}{x})}^{2}} (9 (- x^{- 2})) + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.5

Multiply $- 1$ by $9$ .

$\frac{1}{1 + {(\frac{9}{x})}^{2}} (- 9 x^{- 2}) + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.6

Combine $- 9$ and $\frac{1}{1 + {(\frac{9}{x})}^{2}}$ .

$\frac{- 9}{1 + {(\frac{9}{x})}^{2}} x^{- 2} + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.7

Combine $\frac{- 9}{1 + {(\frac{9}{x})}^{2}}$ and $x^{- 2}$ .

$\frac{- 9 x^{- 2}}{1 + {(\frac{9}{x})}^{2}} + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.8

Move $x^{- 2}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$\frac{- 9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 2.9

Move the negative in front of the fraction.

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{d}{d x} [\arctan (\frac{3}{x})]$

Step 3

Evaluate $\frac{d}{d x} [\arctan (\frac{3}{x})]$ .

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Step 3.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \arctan (x)$ and $g (x) = \frac{3}{x}$ .

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Step 3.1.1

To apply the Chain Rule, set $u_{2}$ as $\frac{3}{x}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{d}{d u_{2}} [\arctan (u_{2})] \frac{d}{d x} [\frac{3}{x}]$

Step 3.1.2

The derivative of $\arctan (u_{2})$ with respect to $u_{2}$ is $\frac{1}{1 + {u_{2}}^{2}}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {u_{2}}^{2}} \frac{d}{d x} [\frac{3}{x}]$

Step 3.1.3

Replace all occurrences of $u_{2}$ with $\frac{3}{x}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {(\frac{3}{x})}^{2}} \frac{d}{d x} [\frac{3}{x}]$

Step 3.2

Since $3$ is constant with respect to $x$ , the derivative of $\frac{3}{x}$ with respect to $x$ is $3 \frac{d}{d x} [\frac{1}{x}]$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {(\frac{3}{x})}^{2}} (3 \frac{d}{d x} [\frac{1}{x}])$

Step 3.3

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

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {(\frac{3}{x})}^{2}} (3 \frac{d}{d x} [x^{- 1}])$

Step 3.4

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

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {(\frac{3}{x})}^{2}} (3 (- x^{- 2}))$

Step 3.5

Multiply $- 1$ by $3$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{1}{1 + {(\frac{3}{x})}^{2}} (- 3 x^{- 2})$

Step 3.6

Combine $- 3$ and $\frac{1}{1 + {(\frac{3}{x})}^{2}}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{- 3}{1 + {(\frac{3}{x})}^{2}} x^{- 2}$

Step 3.7

Combine $\frac{- 3}{1 + {(\frac{3}{x})}^{2}}$ and $x^{- 2}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{- 3 x^{- 2}}{1 + {(\frac{3}{x})}^{2}}$

Step 3.8

Move $x^{- 2}$ to the denominator using the negative exponent rule $b^{- n} = \frac{1}{b^{n}}$ .

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} + \frac{- 3}{(1 + {(\frac{3}{x})}^{2}) x^{2}}$

Step 3.9

Move the negative in front of the fraction.

$- \frac{9}{(1 + {(\frac{9}{x})}^{2}) x^{2}} - \frac{3}{(1 + {(\frac{3}{x})}^{2}) x^{2}}$

Step 4

Simplify.

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Step 4.1

Apply the product rule to $\frac{9}{x}$ .

$- \frac{9}{(1 + \frac{9^{2}}{x^{2}}) x^{2}} - \frac{3}{(1 + {(\frac{3}{x})}^{2}) x^{2}}$

Step 4.2

Apply the product rule to $\frac{3}{x}$ .

$- \frac{9}{(1 + \frac{9^{2}}{x^{2}}) x^{2}} - \frac{3}{(1 + \frac{3^{2}}{x^{2}}) x^{2}}$

Step 4.3

Apply the distributive property.

$- \frac{9}{1 x^{2} + \frac{9^{2}}{x^{2}} x^{2}} - \frac{3}{(1 + \frac{3^{2}}{x^{2}}) x^{2}}$

Step 4.4

Apply the distributive property.

$- \frac{9}{1 x^{2} + \frac{9^{2}}{x^{2}} x^{2}} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5

Combine terms.

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Step 4.5.1

Multiply $x^{2}$ by $1$ .

$- \frac{9}{x^{2} + \frac{9^{2}}{x^{2}} x^{2}} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.2

Raise $9$ to the power of $2$ .

$- \frac{9}{x^{2} + \frac{81}{x^{2}} x^{2}} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.3

Combine $\frac{81}{x^{2}}$ and $x^{2}$ .

$- \frac{9}{x^{2} + \frac{81 x^{2}}{x^{2}}} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.4

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

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Step 4.5.4.1

Cancel the common factor.

$- \frac{9}{x^{2} + \frac{81 x^{2}}{x^{2}}} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.4.2

Divide $81$ by $1$ .

$- \frac{9}{x^{2} + 81} - \frac{3}{1 x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.5

Multiply $x^{2}$ by $1$ .

$- \frac{9}{x^{2} + 81} - \frac{3}{x^{2} + \frac{3^{2}}{x^{2}} x^{2}}$

Step 4.5.6

Raise $3$ to the power of $2$ .

$- \frac{9}{x^{2} + 81} - \frac{3}{x^{2} + \frac{9}{x^{2}} x^{2}}$

Step 4.5.7

Combine $\frac{9}{x^{2}}$ and $x^{2}$ .

$- \frac{9}{x^{2} + 81} - \frac{3}{x^{2} + \frac{9 x^{2}}{x^{2}}}$

Step 4.5.8

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

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Step 4.5.8.1

Cancel the common factor.

$- \frac{9}{x^{2} + 81} - \frac{3}{x^{2} + \frac{9 x^{2}}{x^{2}}}$

Step 4.5.8.2

Divide $9$ by $1$ .

$- \frac{9}{x^{2} + 81} - \frac{3}{x^{2} + 9}$

Step 4.5.9

To write $- \frac{9}{x^{2} + 81}$ as a fraction with a common denominator, multiply by $\frac{x^{2} + 9}{x^{2} + 9}$ .

$- \frac{9}{x^{2} + 81} \cdot \frac{x^{2} + 9}{x^{2} + 9} - \frac{3}{x^{2} + 9}$

Step 4.5.10

To write $- \frac{3}{x^{2} + 9}$ as a fraction with a common denominator, multiply by $\frac{x^{2} + 81}{x^{2} + 81}$ .

$- \frac{9}{x^{2} + 81} \cdot \frac{x^{2} + 9}{x^{2} + 9} - \frac{3}{x^{2} + 9} \cdot \frac{x^{2} + 81}{x^{2} + 81}$

Step 4.5.11

Write each expression with a common denominator of $(x^{2} + 81) (x^{2} + 9)$ , by multiplying each by an appropriate factor of $1$ .

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Step 4.5.11.1

Multiply $\frac{9}{x^{2} + 81}$ by $\frac{x^{2} + 9}{x^{2} + 9}$ .

$- \frac{9 (x^{2} + 9)}{(x^{2} + 81) (x^{2} + 9)} - \frac{3}{x^{2} + 9} \cdot \frac{x^{2} + 81}{x^{2} + 81}$

Step 4.5.11.2

Multiply $\frac{3}{x^{2} + 9}$ by $\frac{x^{2} + 81}{x^{2} + 81}$ .

$- \frac{9 (x^{2} + 9)}{(x^{2} + 81) (x^{2} + 9)} - \frac{3 (x^{2} + 81)}{(x^{2} + 9) (x^{2} + 81)}$

Step 4.5.11.3

Reorder the factors of $(x^{2} + 9) (x^{2} + 81)$ .

$- \frac{9 (x^{2} + 9)}{(x^{2} + 81) (x^{2} + 9)} - \frac{3 (x^{2} + 81)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.5.12

Combine the numerators over the common denominator.

$\frac{- 9 (x^{2} + 9) - 3 (x^{2} + 81)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.6

Reorder terms.

$\frac{- 3 (x^{2} + 81) - 9 (x^{2} + 9)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7

Simplify the numerator.

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Step 4.7.1

Factor $- 3$ out of $- 3 (x^{2} + 81) - 9 (x^{2} + 9)$ .

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Step 4.7.1.1

Factor $- 3$ out of $- 9 (x^{2} + 9)$ .

$\frac{- 3 (x^{2} + 81) - 3 (3 (x^{2} + 9))}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.1.2

Factor $- 3$ out of $- 3 (x^{2} + 81) - 3 (3 (x^{2} + 9))$ .

$\frac{- 3 (x^{2} + 81 + 3 (x^{2} + 9))}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.2

Apply the distributive property.

$\frac{- 3 (x^{2} + 81 + 3 x^{2} + 3 \cdot 9)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.3

Multiply $3$ by $9$ .

$\frac{- 3 (x^{2} + 81 + 3 x^{2} + 27)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.4

Add $x^{2}$ and $3 x^{2}$ .

$\frac{- 3 (4 x^{2} + 81 + 27)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.5

Add $81$ and $27$ .

$\frac{- 3 (4 x^{2} + 108)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.6

Factor $4$ out of $4 x^{2} + 108$ .

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Step 4.7.6.1

Factor $4$ out of $4 x^{2}$ .

$\frac{- 3 (4 (x^{2}) + 108)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.6.2

Factor $4$ out of $108$ .

$\frac{- 3 (4 x^{2} + 4 \cdot 27)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.6.3

Factor $4$ out of $4 x^{2} + 4 \cdot 27$ .

$\frac{- 3 (4 (x^{2} + 27))}{(x^{2} + 81) (x^{2} + 9)}$

$\frac{- 3 \cdot 4 (x^{2} + 27)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.7.7

Multiply $- 3$ by $4$ .

$\frac{- 12 (x^{2} + 27)}{(x^{2} + 81) (x^{2} + 9)}$

Step 4.8

Move the negative in front of the fraction.

$- \frac{12 (x^{2} + 27)}{(x^{2} + 81) (x^{2} + 9)}$