Solve by Factoring x^(2/3)-2x^(1/3)-8=0

$x^{\frac{2}{3}} - 2 x^{\frac{1}{3}} - 8 = 0$

Step 1

Rewrite $x^{\frac{2}{3}}$ as ${(x^{\frac{1}{3}})}^{2}$ .

${(x^{\frac{1}{3}})}^{2} - 2 x^{\frac{1}{3}} - 8 = 0$

Step 2

Let $u = x^{\frac{1}{3}}$ . Substitute $u$ for all occurrences of $x^{\frac{1}{3}}$ .

$u^{2} - 2 u - 8 = 0$

Step 3

Factor $u^{2} - 2 u - 8$ 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 $- 8$ and whose sum is $- 2$ .

$- 4, 2$

Write the factored form using these integers.

$(u - 4) (u + 2) = 0$

Step 4

Replace all occurrences of $u$ with $x^{\frac{1}{3}}$ .

$(x^{\frac{1}{3}} - 4) (x^{\frac{1}{3}} + 2) = 0$

Step 5

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

$x^{\frac{1}{3}} - 4 = 0$

$x^{\frac{1}{3}} + 2 = 0$

Step 6

Set $x^{\frac{1}{3}} - 4$ equal to $0$ and solve for $x$ .

Set $x^{\frac{1}{3}} - 4$ equal to $0$ .

$x^{\frac{1}{3}} - 4 = 0$

Solve $x^{\frac{1}{3}} - 4 = 0$ for $x$ .

Add $4$ to both sides of the equation.

$x^{\frac{1}{3}} = 4$

Raise each side of the equation to the power of $3$ to eliminate the fractional exponent on the left side.

${(x^{\frac{1}{3}})}^{3} = 4^{3}$

Simplify the exponent.

Simplify the left side.

Simplify ${(x^{\frac{1}{3}})}^{3}$ .

Multiply the exponents in ${(x^{\frac{1}{3}})}^{3}$ .

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$x^{\frac{1}{3} \cdot 3} = 4^{3}$

Cancel the common factor of $3$ .

Cancel the common factor.

$x^{\frac{1}{3} \cdot 3} = 4^{3}$

Rewrite the expression.

$x^{1} = 4^{3}$

Simplify.

$x = 4^{3}$

Simplify the right side.

Raise $4$ to the power of $3$ .

$x = 64$

Step 7

Set $x^{\frac{1}{3}} + 2$ equal to $0$ and solve for $x$ .

Set $x^{\frac{1}{3}} + 2$ equal to $0$ .

$x^{\frac{1}{3}} + 2 = 0$

Solve $x^{\frac{1}{3}} + 2 = 0$ for $x$ .

Subtract $2$ from both sides of the equation.

$x^{\frac{1}{3}} = - 2$

Raise each side of the equation to the power of $3$ to eliminate the fractional exponent on the left side.

${(x^{\frac{1}{3}})}^{3} = {(- 2)}^{3}$

Simplify the exponent.

Simplify the left side.

Simplify ${(x^{\frac{1}{3}})}^{3}$ .

Multiply the exponents in ${(x^{\frac{1}{3}})}^{3}$ .

Apply the power rule and multiply exponents, ${(a^{m})}^{n} = a^{m n}$ .

$x^{\frac{1}{3} \cdot 3} = {(- 2)}^{3}$

Cancel the common factor of $3$ .

Cancel the common factor.

$x^{\frac{1}{3} \cdot 3} = {(- 2)}^{3}$

Rewrite the expression.

$x^{1} = {(- 2)}^{3}$

Simplify.

$x = {(- 2)}^{3}$

Simplify the right side.

Raise $- 2$ to the power of $3$ .

$x = - 8$

Step 8

The final solution is all the values that make $(x^{\frac{1}{3}} - 4) (x^{\frac{1}{3}} + 2) = 0$ true.

$x = 64, - 8$

Solve by Factoring x^(2/3)-2x^(1/3)-8=0

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