Factor x^8-17x^4+16

$x^{8} - 17 x^{4} + 16$

Rewrite $x^{8}$ as ${(x^{4})}^{2}$ .

${(x^{4})}^{2} - 17 x^{4} + 16$

Let $u = x^{4}$ . Substitute $u$ for all occurrences of $x^{4}$ .

$u^{2} - 17 u + 16$

Factor $u^{2} - 17 u + 16$ using the AC method.

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 $16$ and whose sum is $- 17$ .

$- 16, - 1$

Write the factored form using these integers.

$(u - 16) (u - 1)$

Replace all occurrences of $u$ with $x^{4}$ .

$(x^{4} - 16) (x^{4} - 1)$

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

$({(x^{2})}^{2} - 16) (x^{4} - 1)$

Rewrite $16$ as $4^{2}$ .

$({(x^{2})}^{2} - 4^{2}) (x^{4} - 1)$

Since both terms are perfect squares, factor using the difference of squares formula, $a^{2} - b^{2} = (a + b) (a - b)$ where $a = x^{2}$ and $b = 4$ .

$(x^{2} + 4) (x^{2} - 4) (x^{4} - 1)$

Simplify.

Rewrite $4$ as $2^{2}$ .

$(x^{2} + 4) (x^{2} - 2^{2}) (x^{4} - 1)$

Factor.

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 $b = 2$ .

$(x^{2} + 4) ((x + 2) (x - 2)) (x^{4} - 1)$

Remove unnecessary parentheses.

$(x^{2} + 4) (x + 2) (x - 2) (x^{4} - 1)$

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

$(x^{2} + 4) (x + 2) (x - 2) ({(x^{2})}^{2} - 1)$

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

$(x^{2} + 4) (x + 2) (x - 2) ({(x^{2})}^{2} - 1^{2})$

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

$(x^{2} + 4) (x + 2) (x - 2) ((x^{2} + 1) (x^{2} - 1))$

Factor.

Simplify.

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

$(x^{2} + 4) (x + 2) (x - 2) ((x^{2} + 1) (x^{2} - 1^{2}))$

Factor.

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 $b = 1$ .

$(x^{2} + 4) (x + 2) (x - 2) ((x^{2} + 1) ((x + 1) (x - 1)))$

Remove unnecessary parentheses.

$(x^{2} + 4) (x + 2) (x - 2) ((x^{2} + 1) (x + 1) (x - 1))$

Remove unnecessary parentheses.

$(x^{2} + 4) (x + 2) (x - 2) (x^{2} + 1) (x + 1) (x - 1)$

Factor x^8-17x^4+16

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