Solve by Factoring x^3-5x^2-4x+20=0

$x^{3} - 5 x^{2} - 4 x + 20 = 0$

Step 1

Factor out the greatest common factor from each group.

Group the first two terms and the last two terms.

$(x^{3} - 5 x^{2}) - 4 x + 20 = 0$

Factor out the greatest common factor (GCF) from each group.

$x^{2} (x - 5) - 4 (x - 5) = 0$

Step 2

Factor the polynomial by factoring out the greatest common factor, $x - 5$ .

$(x - 5) (x^{2} - 4) = 0$

Step 3

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

$(x - 5) (x^{2} - 2^{2}) = 0$

Step 4

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 $b = 2$ .

$(x - 5) ((x + 2) (x - 2)) = 0$

Remove unnecessary parentheses.

$(x - 5) (x + 2) (x - 2) = 0$

Step 5

If any individual factor on the left side of the equation is equal to $0$ , the entire expression will be equal to $0$ .

$x - 5 = 0$

$x + 2 = 0$

$x - 2 = 0$

Step 6

Set $x - 5$ equal to $0$ and solve for $x$ .

Set $x - 5$ equal to $0$ .

$x - 5 = 0$

Add $5$ to both sides of the equation.

$x = 5$

Step 7

Set $x + 2$ equal to $0$ and solve for $x$ .

Set $x + 2$ equal to $0$ .

$x + 2 = 0$

Subtract $2$ from both sides of the equation.

$x = - 2$

Step 8

Set $x - 2$ equal to $0$ and solve for $x$ .

Set $x - 2$ equal to $0$ .

$x - 2 = 0$

Add $2$ to both sides of the equation.

$x = 2$

Step 9

The final solution is all the values that make $(x - 5) (x + 2) (x - 2) = 0$ true.

$x = 5, - 2, 2$