Trigonometry Examples

$f (x) = x^{4} - 4 x^{3} - 4 x^{2} + 36 x - 45$

Step 1

Regroup terms.

$f (x) = - 4 x^{3} + 36 x + x^{4} - 4 x^{2} - 45$

Step 2

Factor $- 4 x$ out of $- 4 x^{3} + 36 x$ .

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Step 2.1

Factor $- 4 x$ out of $- 4 x^{3}$ .

$f (x) = - 4 x \cdot x^{2} + 36 x + x^{4} - 4 x^{2} - 45$

Step 2.2

Factor $- 4 x$ out of $36 x$ .

$f (x) = - 4 x \cdot x^{2} - 4 x \cdot - 9 + x^{4} - 4 x^{2} - 45$

Step 2.3

Factor $- 4 x$ out of $- 4 x (x^{2}) - 4 x (- 9)$ .

$f (x) = - 4 x (x^{2} - 9) + x^{4} - 4 x^{2} - 45$

Step 3

Rewrite $9$ as $3^{2}$ .

$f (x) = - 4 x (x^{2} - 3^{2}) + x^{4} - 4 x^{2} - 45$

Step 4

Factor.

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Step 4.1

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 $b = 3$ .

$f (x) = - 4 x ((x + 3) (x - 3)) + x^{4} - 4 x^{2} - 45$

Step 4.2

Remove unnecessary parentheses.

$f (x) = - 4 x (x + 3) (x - 3) + x^{4} - 4 x^{2} - 45$

Step 5

Rewrite $x^{4}$ as ${(x^{2})}^{2}$ .

$f (x) = - 4 x (x + 3) (x - 3) + {(x^{2})}^{2} - 4 x^{2} - 45$

Step 6

Let $u = x^{2}$ . Substitute $u$ for all occurrences of $x^{2}$ .

$f (x) = - 4 x (x + 3) (x - 3) + u^{2} - 4 u - 45$

Step 7

Factor $u^{2} - 4 u - 45$ using the AC method.

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Step 7.1

Consider the form $x^{2} + b x + c$ . Find a pair of integers whose product is $c$ and whose sum is $b$ . In this case, whose product is $- 45$ and whose sum is $- 4$ .

$- 9, 5$

Step 7.2

Write the factored form using these integers.

$f (x) = - 4 x (x + 3) (x - 3) + (u - 9) (u + 5)$

Step 8

Replace all occurrences of $u$ with $x^{2}$ .

$f (x) = - 4 x (x + 3) (x - 3) + (x^{2} - 9) (x^{2} + 5)$

Step 9

Rewrite $9$ as $3^{2}$ .

$f (x) = - 4 x (x + 3) (x - 3) + (x^{2} - 3^{2}) (x^{2} + 5)$

Step 10

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 $b = 3$ .

$f (x) = - 4 x (x + 3) (x - 3) + (x + 3) (x - 3) (x^{2} + 5)$

Step 11

Factor $(x + 3) (x - 3)$ out of $- 4 x (x + 3) (x - 3) + (x + 3) (x - 3) (x^{2} + 5)$ .

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Step 11.1

Factor $(x + 3) (x - 3)$ out of $- 4 x (x + 3) (x - 3)$ .

$f (x) = (x + 3) (x - 3) (- 4 x) + (x + 3) (x - 3) (x^{2} + 5)$

Step 11.2

Factor $(x + 3) (x - 3)$ out of $(x + 3) (x - 3) (- 4 x) + (x + 3) (x - 3) (x^{2} + 5)$ .

$f (x) = (x + 3) (x - 3) (- 4 x + x^{2} + 5)$

Step 12

Reorder terms.

$f (x) = (x + 3) (x - 3) (x^{2} - 4 x + 5)$