Solve by Factoring x^3+2x^2-36x-72=0

$x^{3} + 2 x^{2} - 36 x - 72 = 0$

Step 1

Factor out the greatest common factor from each group.

Group the first two terms and the last two terms.

$(x^{3} + 2 x^{2}) - 36 x - 72 = 0$

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

$x^{2} (x + 2) - 36 (x + 2) = 0$

Step 2

Factor the polynomial by factoring out the greatest common factor, $x + 2$ .

$(x + 2) (x^{2} - 36) = 0$

Step 3

Rewrite $36$ as $6^{2}$ .

$(x + 2) (x^{2} - 6^{2}) = 0$

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 $b = 6$ .

$(x + 2) ((x + 6) (x - 6)) = 0$

Remove unnecessary parentheses.

$(x + 2) (x + 6) (x - 6) = 0$

Step 5

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

$x + 2 = 0$

$x + 6 = 0$

$x - 6 = 0$

Step 6

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 7

Set $x + 6$ equal to $0$ and solve for $x$ .

Set $x + 6$ equal to $0$ .

$x + 6 = 0$

Subtract $6$ from both sides of the equation.

$x = - 6$

Step 8

Set $x - 6$ equal to $0$ and solve for $x$ .

Set $x - 6$ equal to $0$ .

$x - 6 = 0$

Add $6$ to both sides of the equation.

$x = 6$

Step 9

The final solution is all the values that make $(x + 2) (x + 6) (x - 6) = 0$ true.

$x = - 2, - 6, 6$