Find the Derivative Using Quotient Rule - d/dx

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

Step 1

Differentiate using the Quotient Rule which states that $\frac{d}{d x} [\frac{f (x)}{g (x)}]$ is $\frac{g (x) \frac{d}{d x} [f (x)] - f (x) \frac{d}{d x} [g (x)]}{{g (x)}^{2}}$ where $f (x) = x + 3$ and $g (x) = x^{2} - 1$ .

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

Step 2

Differentiate.

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Step 2.1

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

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

Step 2.2

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

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

Step 2.3

Since $3$ is constant with respect to $x$ , the derivative of $3$ with respect to $x$ is $0$ .

$\frac{(x^{2} - 1) (1 + 0) - (x + 3) \frac{d}{d x} [x^{2} - 1]}{{(x^{2} - 1)}^{2}}$

Step 2.4

Add $1$ and $0$ .

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

Step 2.5

By the Sum Rule, the derivative of $x^{2} - 1$ with respect to $x$ is $\frac{d}{d x} [x^{2}] + \frac{d}{d x} [- 1]$ .

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

Step 2.6

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

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

Step 2.7

Since $- 1$ is constant with respect to $x$ , the derivative of $- 1$ with respect to $x$ is $0$ .

$\frac{(x^{2} - 1) \cdot 1 - (x + 3) (2 x + 0)}{{(x^{2} - 1)}^{2}}$

Step 2.8

Add $2 x$ and $0$ .

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

Step 3

Simplify.

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Step 3.1

Apply the distributive property.

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

Step 3.2

Apply the distributive property.

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

Step 3.3

Apply the distributive property.

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

Step 3.4

Simplify the numerator.

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Step 3.4.1

Simplify each term.

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Step 3.4.1.1

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

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

Step 3.4.1.2

Multiply $- 1$ by $1$ .

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

Step 3.4.1.3

Rewrite using the commutative property of multiplication.

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

Step 3.4.1.4

Multiply $x$ by $x$ by adding the exponents.

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Step 3.4.1.4.1

Move $x$ .

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

Step 3.4.1.4.2

Multiply $x$ by $x$ .

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

Step 3.4.1.5

Multiply $- 1$ by $2$ .

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

Step 3.4.1.6

Multiply $- 1$ by $3$ .

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

Step 3.4.1.7

Multiply $2$ by $- 3$ .

$\frac{x^{2} - 1 - 2 x^{2} - 6 x}{{(x^{2} - 1)}^{2}}$

Step 3.4.2

Subtract $2 x^{2}$ from $x^{2}$ .

$\frac{- x^{2} - 1 - 6 x}{{(x^{2} - 1)}^{2}}$

Step 3.5

Reorder terms.

$\frac{- x^{2} - 6 x - 1}{{(x^{2} - 1)}^{2}}$

Step 3.6

Simplify the denominator.

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Step 3.6.1

Rewrite $1$ as $1^{2}$ .

$\frac{- x^{2} - 6 x - 1}{{(x^{2} - 1^{2})}^{2}}$

Step 3.6.2

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = x$ and $b = 1$ .

$\frac{- x^{2} - 6 x - 1}{{((x + 1) (x - 1))}^{2}}$

Step 3.6.3

Apply the product rule to $(x + 1) (x - 1)$ .

$\frac{- x^{2} - 6 x - 1}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.7

Factor $- 1$ out of $- x^{2}$ .

$\frac{- (x^{2}) - 6 x - 1}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.8

Factor $- 1$ out of $- 6 x$ .

$\frac{- (x^{2}) - (6 x) - 1}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.9

Factor $- 1$ out of $- (x^{2}) - (6 x)$ .

$\frac{- (x^{2} + 6 x) - 1}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.10

Rewrite $- 1$ as $- 1 (1)$ .

$\frac{- (x^{2} + 6 x) - 1 (1)}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.11

Factor $- 1$ out of $- (x^{2} + 6 x) - 1 (1)$ .

$\frac{- (x^{2} + 6 x + 1)}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.12

Rewrite $- (x^{2} + 6 x + 1)$ as $- 1 (x^{2} + 6 x + 1)$ .

$\frac{- 1 (x^{2} + 6 x + 1)}{{(x + 1)}^{2} {(x - 1)}^{2}}$

Step 3.13

Move the negative in front of the fraction.

$- \frac{x^{2} + 6 x + 1}{{(x + 1)}^{2} {(x - 1)}^{2}}$

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Find the Derivative Using Quotient Rule - d/dx

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