Write as a Set of Linear Factors f(x)=x^3-57x+56

$f (x) = x^{3} - 57 x + 56$

Step 1

Factor $x^{3} - 57 x + 56$ using the rational roots test.

If a polynomial function has integer coefficients, then every rational zero will have the form $\frac{p}{q}$ where $p$ is a factor of the constant and $q$ is a factor of the leading coefficient.

$f (x) = p = \pm 1, \pm 56, \pm 2, \pm 28, \pm 4, \pm 14, \pm 7, \pm 8$

$q = \pm 1$

Find every combination of $\pm \frac{p}{q}$ . These are the possible roots of the polynomial function.

$f (x) = \pm 1, \pm 56, \pm 2, \pm 28, \pm 4, \pm 14, \pm 7, \pm 8$

Substitute $1$ and simplify the expression. In this case, the expression is equal to $0$ so $1$ is a root of the polynomial.

Substitute $1$ into the polynomial.

$f (x) = 1^{3} - 57 \cdot 1 + 56$

Raise $1$ to the power of $3$ .

$f (x) = 1 - 57 \cdot 1 + 56$

Multiply $- 57$ by $1$ .

$f (x) = 1 - 57 + 56$

Subtract $57$ from $1$ .

$f (x) = - 56 + 56$

Add $- 56$ and $56$ .

$f (x) = 0$

Since $1$ is a known root, divide the polynomial by $x - 1$ to find the quotient polynomial. This polynomial can then be used to find the remaining roots.

$f (x) = \frac{x^{3} - 57 x + 56}{x - 1}$

Divide $x^{3} - 57 x + 56$ by $x - 1$ .

Set up the polynomials to be divided. If there is not a term for every exponent, insert one with a value of $0$ .

$f (x) =$

Divide the highest order term in the dividend $x^{3}$ by the highest order term in divisor $x$ .

$f (x) =$

Multiply the new quotient term by the divisor.

$f (x) =$

The expression needs to be subtracted from the dividend, so change all the signs in $x^{3} - x^{2}$

$f (x) =$

After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.

$f (x) =$

Pull the next terms from the original dividend down into the current dividend.

$f (x) =$

Divide the highest order term in the dividend $x^{2}$ by the highest order term in divisor $x$ .

$f (x) =$

Multiply the new quotient term by the divisor.

$f (x) =$

The expression needs to be subtracted from the dividend, so change all the signs in $x^{2} - x$

$f (x) =$

After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.

$f (x) =$

Pull the next terms from the original dividend down into the current dividend.

$f (x) =$

Divide the highest order term in the dividend $- 56 x$ by the highest order term in divisor $x$ .

$f (x) =$

Multiply the new quotient term by the divisor.

$f (x) =$

The expression needs to be subtracted from the dividend, so change all the signs in $- 56 x + 56$

$f (x) =$

After changing the signs, add the last dividend from the multiplied polynomial to find the new dividend.

$f (x) =$

Since the remander is $0$ , the final answer is the quotient.

$f (x) = x^{2} + x - 56$

Write $x^{3} - 57 x + 56$ as a set of factors.

$f (x) = (x - 1) (x^{2} + x - 56)$

Step 2

Factor $x^{2} + x - 56$ using the AC method.

Consider the form $x^{2} + i x + c$ . Find a pair of integers whose product is $c$ and whose sum is $i$ . In this case, whose product is $- 56$ and whose sum is $1$ .

$f (x) = - 7, 8$

Write the factored form using these integers.

$f (x) = (x - 1) ((x - 7) (x + 8))$

Remove unnecessary parentheses.

$f (x) = (x - 1) (x - 7) (x + 8)$

Write as a Set of Linear Factors f(x)=x^3-57x+56

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