Calculus Examples

$y = \sec (2 x)$

Step 1

Find the first derivative.

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Step 1.1

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sec (x)$ and $g (x) = 2 x$ .

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Step 1.1.1

To apply the Chain Rule, set $u$ as $2 x$ .

$\frac{d}{d u} [\sec (u)] \frac{d}{d x} [2 x]$

Step 1.1.2

The derivative of $\sec (u)$ with respect to $u$ is $\sec (u) \tan (u)$ .

$\sec (u) \tan (u) \frac{d}{d x} [2 x]$

Step 1.1.3

Replace all occurrences of $u$ with $2 x$ .

$\sec (2 x) \tan (2 x) \frac{d}{d x} [2 x]$

Step 1.2

Differentiate.

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Step 1.2.1

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$\sec (2 x) \tan (2 x) (2 \frac{d}{d x} [x])$

Step 1.2.2

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

$\sec (2 x) \tan (2 x) (2 \cdot 1)$

Step 1.2.3

Simplify the expression.

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Step 1.2.3.1

Multiply $2$ by $1$ .

$\sec (2 x) \tan (2 x) \cdot 2$

Step 1.2.3.2

Move $2$ to the left of $\sec (2 x) \tan (2 x)$ .

$f' (x) = 2 \sec (2 x) \tan (2 x)$

Step 2

Find the second derivative.

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Step 2.1

Since $2$ is constant with respect to $x$ , the derivative of $2 \sec (2 x) \tan (2 x)$ with respect to $x$ is $2 \frac{d}{d x} [\sec (2 x) \tan (2 x)]$ .

$2 \frac{d}{d x} [\sec (2 x) \tan (2 x)]$

Step 2.2

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 $f (x) = \sec (2 x)$ and $g (x) = \tan (2 x)$ .

$2 (\sec (2 x) \frac{d}{d x} [\tan (2 x)] + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \tan (x)$ and $g (x) = 2 x$ .

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Step 2.3.1

To apply the Chain Rule, set $u_{1}$ as $2 x$ .

$2 (\sec (2 x) (\frac{d}{d u_{1}} [\tan (u_{1})] \frac{d}{d x} [2 x]) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.3.2

The derivative of $\tan (u_{1})$ with respect to $u_{1}$ is $\sec^{2} (u_{1})$ .

$2 (\sec (2 x) (\sec^{2} (u_{1}) \frac{d}{d x} [2 x]) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.3.3

Replace all occurrences of $u_{1}$ with $2 x$ .

$2 (\sec (2 x) (\sec^{2} (2 x) \frac{d}{d x} [2 x]) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.4

Raise $\sec (2 x)$ to the power of $1$ .

$2 (\sec^{2} (2 x) \sec^{1} (2 x) \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.5

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

$2 ({\sec (2 x)}^{2 + 1} \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.6

Differentiate.

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Step 2.6.1

Add $2$ and $1$ .

$2 (\sec^{3} (2 x) \frac{d}{d x} [2 x] + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.6.2

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$2 (\sec^{3} (2 x) (2 \frac{d}{d x} [x]) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.6.3

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

$2 (\sec^{3} (2 x) (2 \cdot 1) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.6.4

Simplify the expression.

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Step 2.6.4.1

Multiply $2$ by $1$ .

$2 (\sec^{3} (2 x) \cdot 2 + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.6.4.2

Move $2$ to the left of $\sec^{3} (2 x)$ .

$2 (2 \cdot \sec^{3} (2 x) + \tan (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 2.7

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sec (x)$ and $g (x) = 2 x$ .

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Step 2.7.1

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

$2 (2 \sec^{3} (2 x) + \tan (2 x) (\frac{d}{d u_{2}} [\sec (u_{2})] \frac{d}{d x} [2 x]))$

Step 2.7.2

The derivative of $\sec (u_{2})$ with respect to $u_{2}$ is $\sec (u_{2}) \tan (u_{2})$ .

$2 (2 \sec^{3} (2 x) + \tan (2 x) (\sec (u_{2}) \tan (u_{2}) \frac{d}{d x} [2 x]))$

Step 2.7.3

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

$2 (2 \sec^{3} (2 x) + \tan (2 x) (\sec (2 x) \tan (2 x) \frac{d}{d x} [2 x]))$

Step 2.8

Raise $\tan (2 x)$ to the power of $1$ .

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

Step 2.9

Raise $\tan (2 x)$ to the power of $1$ .

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

Step 2.10

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

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

Step 2.11

Add $1$ and $1$ .

$2 (2 \sec^{3} (2 x) + \tan^{2} (2 x) (\sec (2 x) \frac{d}{d x} [2 x]))$

Step 2.12

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$2 (2 \sec^{3} (2 x) + \tan^{2} (2 x) \sec (2 x) (2 \frac{d}{d x} [x]))$

Step 2.13

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

$2 (2 \sec^{3} (2 x) + \tan^{2} (2 x) \sec (2 x) (2 \cdot 1))$

Step 2.14

Simplify the expression.

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Step 2.14.1

Multiply $2$ by $1$ .

$2 (2 \sec^{3} (2 x) + \tan^{2} (2 x) \sec (2 x) \cdot 2)$

Step 2.14.2

Move $2$ to the left of $\tan^{2} (2 x) \sec (2 x)$ .

$2 (2 \sec^{3} (2 x) + 2 \cdot (\tan^{2} (2 x) \sec (2 x)))$

Step 2.15

Simplify.

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Step 2.15.1

Apply the distributive property.

$2 (2 \sec^{3} (2 x)) + 2 (2 \tan^{2} (2 x) \sec (2 x))$

Step 2.15.2

Combine terms.

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Step 2.15.2.1

Multiply $2$ by $2$ .

$4 \sec^{3} (2 x) + 2 (2 \tan^{2} (2 x) \sec (2 x))$

Step 2.15.2.2

Multiply $2$ by $2$ .

$4 \sec^{3} (2 x) + 4 \tan^{2} (2 x) \sec (2 x)$

Step 2.15.3

Reorder terms.

$f'' (x) = 4 \tan^{2} (2 x) \sec (2 x) + 4 \sec^{3} (2 x)$

Step 3

Find the third derivative.

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Step 3.1

By the Sum Rule, the derivative of $4 \tan^{2} (2 x) \sec (2 x) + 4 \sec^{3} (2 x)$ with respect to $x$ is $\frac{d}{d x} [4 \tan^{2} (2 x) \sec (2 x)] + \frac{d}{d x} [4 \sec^{3} (2 x)]$ .

$\frac{d}{d x} [4 \tan^{2} (2 x) \sec (2 x)] + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2

Evaluate $\frac{d}{d x} [4 \tan^{2} (2 x) \sec (2 x)]$ .

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Step 3.2.1

Since $4$ is constant with respect to $x$ , the derivative of $4 \tan^{2} (2 x) \sec (2 x)$ with respect to $x$ is $4 \frac{d}{d x} [\tan^{2} (2 x) \sec (2 x)]$ .

$4 \frac{d}{d x} [\tan^{2} (2 x) \sec (2 x)] + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.2

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 $f (x) = \tan^{2} (2 x)$ and $g (x) = \sec (2 x)$ .

$4 (\tan^{2} (2 x) \frac{d}{d x} [\sec (2 x)] + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sec (x)$ and $g (x) = 2 x$ .

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Step 3.2.3.1

To apply the Chain Rule, set $u_{1}$ as $2 x$ .

$4 (\tan^{2} (2 x) (\frac{d}{d u_{1}} [\sec (u_{1})] \frac{d}{d x} [2 x]) + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.3.2

The derivative of $\sec (u_{1})$ with respect to $u_{1}$ is $\sec (u_{1}) \tan (u_{1})$ .

$4 (\tan^{2} (2 x) (\sec (u_{1}) \tan (u_{1}) \frac{d}{d x} [2 x]) + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.3.3

Replace all occurrences of $u_{1}$ with $2 x$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) \frac{d}{d x} [2 x]) + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.4

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \frac{d}{d x} [x])) + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.5

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

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) \frac{d}{d x} [\tan^{2} (2 x)]) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.6

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{2}$ and $g (x) = \tan (2 x)$ .

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Step 3.2.6.1

To apply the Chain Rule, set $u_{2}$ as $\tan (2 x)$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (\frac{d}{d u_{2}} [{u_{2}}^{2}] \frac{d}{d x} [\tan (2 x)])) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.6.2

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

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 u_{2} \frac{d}{d x} [\tan (2 x)])) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.6.3

Replace all occurrences of $u_{2}$ with $\tan (2 x)$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) \frac{d}{d x} [\tan (2 x)])) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.7

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \tan (x)$ and $g (x) = 2 x$ .

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Step 3.2.7.1

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

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) (\frac{d}{d u_{3}} [\tan (u_{3})] \frac{d}{d x} [2 x]))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.7.2

The derivative of $\tan (u_{3})$ with respect to $u_{3}$ is $\sec^{2} (u_{3})$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (u_{3}) \frac{d}{d x} [2 x]))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.7.3

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

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) \frac{d}{d x} [2 x]))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.8

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \frac{d}{d x} [x])))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.9

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

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.10

Multiply $2$ by $1$ .

$4 (\tan^{2} (2 x) (\sec (2 x) \tan (2 x) \cdot 2) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.11

Move $2$ to the left of $\sec (2 x) \tan (2 x)$ .

$4 (\tan^{2} (2 x) (2 \cdot (\sec (2 x) \tan (2 x))) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.12

Multiply $\tan^{2} (2 x)$ by $\tan (2 x)$ by adding the exponents.

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Step 3.2.12.1

Move $\tan (2 x)$ .

$4 (\tan (2 x) \tan^{2} (2 x) (2 \sec (2 x)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.12.2

Multiply $\tan (2 x)$ by $\tan^{2} (2 x)$ .

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Step 3.2.12.2.1

Raise $\tan (2 x)$ to the power of $1$ .

$4 (\tan^{1} (2 x) \tan^{2} (2 x) (2 \sec (2 x)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.12.2.2

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

$4 ({\tan (2 x)}^{1 + 2} (2 \sec (2 x)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.12.3

Add $1$ and $2$ .

$4 (\tan^{3} (2 x) (2 \sec (2 x)) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.13

Move $2$ to the left of $\tan^{3} (2 x)$ .

$4 (2 \cdot \tan^{3} (2 x) \sec (2 x) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) (2 \cdot 1)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.14

Multiply $2$ by $1$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + \sec (2 x) (2 \tan (2 x) (\sec^{2} (2 x) \cdot 2))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.15

Move $2$ to the left of $\sec^{2} (2 x)$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + \sec (2 x) (2 \tan (2 x) (2 \cdot \sec^{2} (2 x)))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.16

Multiply $2$ by $2$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + \sec (2 x) (4 \tan (2 x) \sec^{2} (2 x))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.17

Raise $\sec (2 x)$ to the power of $1$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) (\sec^{1} (2 x) \sec^{2} (2 x))) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.18

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

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) {\sec (2 x)}^{1 + 2}) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.2.19

Add $1$ and $2$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + \frac{d}{d x} [4 \sec^{3} (2 x)]$

Step 3.3

Evaluate $\frac{d}{d x} [4 \sec^{3} (2 x)]$ .

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Step 3.3.1

Since $4$ is constant with respect to $x$ , the derivative of $4 \sec^{3} (2 x)$ with respect to $x$ is $4 \frac{d}{d x} [\sec^{3} (2 x)]$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 \frac{d}{d x} [\sec^{3} (2 x)]$

Step 3.3.2

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = x^{3}$ and $g (x) = \sec (2 x)$ .

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Step 3.3.2.1

To apply the Chain Rule, set $u_{4}$ as $\sec (2 x)$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (\frac{d}{d u_{4}} [{u_{4}}^{3}] \frac{d}{d x} [\sec (2 x)])$

Step 3.3.2.2

Differentiate using the Power Rule which states that $\frac{d}{d u_{4}} [{u_{4}}^{n}]$ is $n {u_{4}}^{n - 1}$ where $n = 3$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 {u_{4}}^{2} \frac{d}{d x} [\sec (2 x)])$

Step 3.3.2.3

Replace all occurrences of $u_{4}$ with $\sec (2 x)$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) \frac{d}{d x} [\sec (2 x)])$

Step 3.3.3

Differentiate using the chain rule, which states that $\frac{d}{d x} [f (g (x))]$ is $f' (g (x)) g' (x)$ where $f (x) = \sec (x)$ and $g (x) = 2 x$ .

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Step 3.3.3.1

To apply the Chain Rule, set $u_{5}$ as $2 x$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\frac{d}{d u_{5}} [\sec (u_{5})] \frac{d}{d x} [2 x]))$

Step 3.3.3.2

The derivative of $\sec (u_{5})$ with respect to $u_{5}$ is $\sec (u_{5}) \tan (u_{5})$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\sec (u_{5}) \tan (u_{5}) \frac{d}{d x} [2 x]))$

Step 3.3.3.3

Replace all occurrences of $u_{5}$ with $2 x$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\sec (2 x) \tan (2 x) \frac{d}{d x} [2 x]))$

Step 3.3.4

Since $2$ is constant with respect to $x$ , the derivative of $2 x$ with respect to $x$ is $2 \frac{d}{d x} [x]$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \frac{d}{d x} [x])))$

Step 3.3.5

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

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\sec (2 x) \tan (2 x) (2 \cdot 1)))$

Step 3.3.6

Multiply $2$ by $1$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (\sec (2 x) \tan (2 x) \cdot 2))$

Step 3.3.7

Move $2$ to the left of $\sec (2 x) \tan (2 x)$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (3 \sec^{2} (2 x) (2 \cdot (\sec (2 x) \tan (2 x))))$

Step 3.3.8

Multiply $2$ by $3$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (6 \sec^{2} (2 x) (\sec (2 x) \tan (2 x)))$

Step 3.3.9

Raise $\sec (2 x)$ to the power of $1$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (6 (\sec^{1} (2 x) \sec^{2} (2 x)) \tan (2 x))$

Step 3.3.10

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

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (6 {\sec (2 x)}^{1 + 2} \tan (2 x))$

Step 3.3.11

Add $1$ and $2$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 4 (6 \sec^{3} (2 x) \tan (2 x))$

Step 3.3.12

Multiply $6$ by $4$ .

$4 (2 \tan^{3} (2 x) \sec (2 x) + 4 \tan (2 x) \sec^{3} (2 x)) + 24 \sec^{3} (2 x) \tan (2 x)$

Step 3.4

Simplify.

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Step 3.4.1

Apply the distributive property.

$4 (2 \tan^{3} (2 x) \sec (2 x)) + 4 (4 \tan (2 x) \sec^{3} (2 x)) + 24 \sec^{3} (2 x) \tan (2 x)$

Step 3.4.2

Combine terms.

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Step 3.4.2.1

Multiply $2$ by $4$ .

$8 (\tan^{3} (2 x) \sec (2 x)) + 4 (4 \tan (2 x) \sec^{3} (2 x)) + 24 \sec^{3} (2 x) \tan (2 x)$

Step 3.4.2.2

Multiply $4$ by $4$ .

$8 \tan^{3} (2 x) \sec (2 x) + 16 (\tan (2 x) \sec^{3} (2 x)) + 24 \sec^{3} (2 x) \tan (2 x)$

Step 3.4.2.3

Reorder the factors of $16 \tan (2 x) \sec^{3} (2 x)$ .

$8 \tan^{3} (2 x) \sec (2 x) + 16 \sec^{3} (2 x) \tan (2 x) + 24 \sec^{3} (2 x) \tan (2 x)$

Step 3.4.2.4

Add $16 \sec^{3} (2 x) \tan (2 x)$ and $24 \sec^{3} (2 x) \tan (2 x)$ .

$f''' (x) = 8 \tan^{3} (2 x) \sec (2 x) + 40 \sec^{3} (2 x) \tan (2 x)$