Solve by Factoring 81x^2-144=0

$81 x^{2} - 144 = 0$

Step 1

Factor $9$ out of $81 x^{2} - 144$ .

Factor $9$ out of $81 x^{2}$ .

$9 (9 x^{2}) - 144 = 0$

Factor $9$ out of $- 144$ .

$9 (9 x^{2}) + 9 (- 16) = 0$

Factor $9$ out of $9 (9 x^{2}) + 9 (- 16)$ .

$9 (9 x^{2} - 16) = 0$

Step 2

Rewrite $9 x^{2}$ as ${(3 x)}^{2}$ .

$9 ({(3 x)}^{2} - 16) = 0$

Step 3

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

$9 ({(3 x)}^{2} - 4^{2}) = 0$

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 $a = 3 x$ and $b = 4$ .

$9 ((3 x + 4) (3 x - 4)) = 0$

Remove unnecessary parentheses.

$9 (3 x + 4) (3 x - 4) = 0$

Step 5

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

$3 x + 4 = 0$

$3 x - 4 = 0$

Step 6

Set $3 x + 4$ equal to $0$ and solve for $x$ .

Set $3 x + 4$ equal to $0$ .

$3 x + 4 = 0$

Solve $3 x + 4 = 0$ for $x$ .

Subtract $4$ from both sides of the equation.

$3 x = - 4$

Divide each term in $3 x = - 4$ by $3$ and simplify.

Divide each term in $3 x = - 4$ by $3$ .

$\frac{3 x}{3} = \frac{- 4}{3}$

Simplify the left side.

Cancel the common factor of $3$ .

Cancel the common factor.

$\frac{3 x}{3} = \frac{- 4}{3}$

Divide $x$ by $1$ .

$x = \frac{- 4}{3}$

Simplify the right side.

Move the negative in front of the fraction.

$x = - \frac{4}{3}$

Step 7

Set $3 x - 4$ equal to $0$ and solve for $x$ .

Set $3 x - 4$ equal to $0$ .

$3 x - 4 = 0$

Solve $3 x - 4 = 0$ for $x$ .

Add $4$ to both sides of the equation.

$3 x = 4$

Divide each term in $3 x = 4$ by $3$ and simplify.

Divide each term in $3 x = 4$ by $3$ .

$\frac{3 x}{3} = \frac{4}{3}$

Simplify the left side.

Cancel the common factor of $3$ .

Cancel the common factor.

$\frac{3 x}{3} = \frac{4}{3}$

Divide $x$ by $1$ .

$x = \frac{4}{3}$

Step 8

The final solution is all the values that make $9 (3 x + 4) (3 x - 4) = 0$ true.

$x = - \frac{4}{3}, \frac{4}{3}$

Solve by Factoring 81x^2-144=0

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