Calculus Examples

$x^{2} \arctan (9 x)$

Step 1

Differentiate using the Product Rule which states that $\frac{d}{d x} [f (x) g (x)]$ is $f (x) \frac{d}{d x} [g (x)] + g (x) \frac{d}{d x} [f (x)]$ where $f (x) = x^{2}$ and $g (x) = \arctan (9 x)$ .

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

Step 2

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 $g (x) = 9 x$ .

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Step 2.1

To apply the Chain Rule, set $u$ as $9 x$ .

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

Step 2.2

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

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

Step 2.3

Replace all occurrences of $u$ with $9 x$ .

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

Step 3

Differentiate.

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Step 3.1

Factor $9$ out of $9 x$ .

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

Step 3.2

Combine fractions.

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Step 3.2.1

Simplify the expression.

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Step 3.2.1.1

Apply the product rule to $9 (x)$ .

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

Step 3.2.1.2

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

$x^{2} (\frac{1}{1 + 81 x^{2}} \frac{d}{d x} [9 x]) + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.2.2

Combine $\frac{1}{1 + 81 x^{2}}$ and $x^{2}$ .

$\frac{x^{2}}{1 + 81 x^{2}} \frac{d}{d x} [9 x] + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.3

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

$\frac{x^{2}}{1 + 81 x^{2}} (9 \frac{d}{d x} [x]) + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.4

Combine $9$ and $\frac{x^{2}}{1 + 81 x^{2}}$ .

$\frac{9 x^{2}}{1 + 81 x^{2}} \frac{d}{d x} [x] + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.5

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

$\frac{9 x^{2}}{1 + 81 x^{2}} \cdot 1 + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.6

Multiply $\frac{9 x^{2}}{1 + 81 x^{2}}$ by $1$ .

$\frac{9 x^{2}}{1 + 81 x^{2}} + \arctan (9 x) \frac{d}{d x} [x^{2}]$

Step 3.7

Differentiate using the Power Rule which states that $\frac{d}{d x} [x^{n}]$ is $n x^{n - 1}$ where $n = 2$ .

$\frac{9 x^{2}}{1 + 81 x^{2}} + \arctan (9 x) (2 x)$

Step 4

To write $\arctan (9 x) (2 x)$ as a fraction with a common denominator, multiply by $\frac{1 + 81 x^{2}}{1 + 81 x^{2}}$ .

$\frac{9 x^{2}}{1 + 81 x^{2}} + \frac{\arctan (9 x) (2 x) (1 + 81 x^{2})}{1 + 81 x^{2}}$

Step 5

Combine the numerators over the common denominator.

$\frac{9 x^{2} + \arctan (9 x) (2 x) (1 + 81 x^{2})}{1 + 81 x^{2}}$

Step 6

Simplify.

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Step 6.1

Apply the distributive property.

$\frac{9 x^{2} + \arctan (9 x) (2 x) \cdot 1 + \arctan (9 x) (2 x) (81 x^{2})}{1 + 81 x^{2}}$

Step 6.2

Simplify the numerator.

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Step 6.2.1

Simplify each term.

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Step 6.2.1.1

Rewrite using the commutative property of multiplication.

$\frac{9 x^{2} + 2 \arctan (9 x) x \cdot 1 + \arctan (9 x) (2 x) (81 x^{2})}{1 + 81 x^{2}}$

Step 6.2.1.2

Multiply $2$ by $1$ .

$\frac{9 x^{2} + 2 \arctan (9 x) x + \arctan (9 x) (2 x) (81 x^{2})}{1 + 81 x^{2}}$

Step 6.2.1.3

Multiply $x$ by $x^{2}$ by adding the exponents.

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Step 6.2.1.3.1

Move $x^{2}$ .

$\frac{9 x^{2} + 2 \arctan (9 x) x + \arctan (9 x) (2 (x^{2} x)) \cdot 81}{1 + 81 x^{2}}$

Step 6.2.1.3.2

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

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Step 6.2.1.3.2.1

Raise $x$ to the power of $1$ .

$\frac{9 x^{2} + 2 \arctan (9 x) x + \arctan (9 x) (2 (x^{2} x^{1})) \cdot 81}{1 + 81 x^{2}}$

Step 6.2.1.3.2.2

Use the power rule $a^{m} a^{n} = a^{m + n}$ to combine exponents.

$\frac{9 x^{2} + 2 \arctan (9 x) x + \arctan (9 x) (2 x^{2 + 1}) \cdot 81}{1 + 81 x^{2}}$

Step 6.2.1.3.3

Add $2$ and $1$ .

$\frac{9 x^{2} + 2 \arctan (9 x) x + \arctan (9 x) (2 x^{3}) \cdot 81}{1 + 81 x^{2}}$

Step 6.2.1.4

Rewrite using the commutative property of multiplication.

$\frac{9 x^{2} + 2 \arctan (9 x) x + 2 \arctan (9 x) x^{3} \cdot 81}{1 + 81 x^{2}}$

Step 6.2.1.5

Multiply $81$ by $2$ .

$\frac{9 x^{2} + 2 \arctan (9 x) x + 162 \arctan (9 x) x^{3}}{1 + 81 x^{2}}$

Step 6.2.2

Reorder factors in $9 x^{2} + 2 \arctan (9 x) x + 162 \arctan (9 x) x^{3}$ .

$\frac{9 x^{2} + 2 x \arctan (9 x) + 162 x^{3} \arctan (9 x)}{1 + 81 x^{2}}$

Step 6.3

Reorder terms.

$\frac{9 x^{2} + 2 x \arctan (9 x) + 162 x^{3} \arctan (9 x)}{81 x^{2} + 1}$