Solve for x x^4-8x^2+7=0

$x^{4} - 8 x^{2} + 7 = 0$

Step 1

Substitute $u = x^{2}$ into the equation. This will make the quadratic formula easy to use.

$u^{2} - 8 u + 7 = 0$

$u = x^{2}$

Step 2

Factor $u^{2} - 8 u + 7$ 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 $7$ and whose sum is $- 8$ .

$- 7, - 1$

Write the factored form using these integers.

$(u - 7) (u - 1) = 0$

Step 3

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

$u - 7 = 0$

$u - 1 = 0$

Step 4

Set $u - 7$ equal to $0$ and solve for $u$ .

Set $u - 7$ equal to $0$ .

$u - 7 = 0$

Add $7$ to both sides of the equation.

$u = 7$

Step 5

Set $u - 1$ equal to $0$ and solve for $u$ .

Set $u - 1$ equal to $0$ .

$u - 1 = 0$

Add $1$ to both sides of the equation.

$u = 1$

Step 6

The final solution is all the values that make $(u - 7) (u - 1) = 0$ true.

$u = 7, 1$

Step 7

Substitute the real value of $u = x^{2}$ back into the solved equation.

$x^{2} = 7$

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

Step 8

Solve the first equation for $x$ .

$x^{2} = 7$

Step 9

Solve the equation for $x$ .

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x = \pm \sqrt{7}$

The complete solution is the result of both the positive and negative portions of the solution.

First, use the positive value of the $\pm$ to find the first solution.

$x = \sqrt{7}$

Next, use the negative value of the $\pm$ to find the second solution.

$x = - \sqrt{7}$

The complete solution is the result of both the positive and negative portions of the solution.

$x = \sqrt{7}, - \sqrt{7}$

Step 10

Solve the second equation for $x$ .

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

Step 11

Solve the equation for $x$ .

Remove parentheses.

$x^{2} = 1$

Take the specified root of both sides of the equation to eliminate the exponent on the left side.

$x = \pm \sqrt{1}$

Any root of $1$ is $1$ .

$x = \pm 1$

The complete solution is the result of both the positive and negative portions of the solution.

First, use the positive value of the $\pm$ to find the first solution.

$x = 1$

Next, use the negative value of the $\pm$ to find the second solution.

$x = - 1$

The complete solution is the result of both the positive and negative portions of the solution.

$x = 1, - 1$

Step 12

The solution to $x^{4} - 8 x^{2} + 7 = 0$ is $x = \sqrt{7}, - \sqrt{7}, 1, - 1$ .

$x = \sqrt{7}, - \sqrt{7}, 1, - 1$

Step 13

The result can be shown in multiple forms.

Exact Form:

$x = \sqrt{7}, - \sqrt{7}, 1, - 1$

Decimal Form:

$x = 2.64575131 \dots, - 2.64575131 \dots, 1, - 1$

Solve for x x^4-8x^2+7=0

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