Solve quadratic equation by completing the square.?

Question

x^2 - 8x -1 =0

Answer 1

x^2 - 8x -1 =0
x^2 -8x +16 -16 -1 =0
(x-4)^2 =17
x-4 = +- sqrt(17)
x= 4 +- sqrt(17) .

Answer 2

x^2 - 8x - 1 = 0

Your first step is to determine WHICH value to add and subtract. The key value here is "half squared" of the coefficient of x.

What is the coefficient of x? It's -8.
Now, we take half of this value (which is -4), and then square it (which is 16). What we're going to do is add 16, and then offset the equation by subtracting 16, like so:

x^2 - 8x + 16 - 1 - 16 = 0

Now, we can factor the first three terms because it is now a square.

(x - 4)^2 - 1 - 16 = 0

Group like terms,

(x - 4)^2 - 17 = 0

Bring the -17 to the right hand side,

(x - 4)^2 = 17

And then take the square root of both sides. **NOTE** When taking the square root of both sides of an equation, it is important to put "plus or minus" on the right hand side.

x - 4 = +/- sqrt(17)

Now, bring the 4 over to the right hand side, to get
x = 4 +/- sqrt(17)

Therefore, our values are x = 4 + sqrt(17), 4 - sqrt(17), or

Answer 3

x² - 8x - 1 = 0

x² - 8 x - 1 + 1 = 0 + 1

x² - 8x + 16 = 1 + 16

x² - 8x + 16 = 17

(x - 4)(x - 4) = 17

(x - 4)² = √17

x - 4 = ± √17

x - 4 + 4 = 4 ± √17

x = 4 ± 4.123105626

- - - - - - -

Solving for +

x = 4 + 4.123105626

x - 8.123105626

- - - - - - - - - - -

Solving for -

x = 4 - 4.123105626

x = 0.123105626

- - - - - -s-

Answer 4

x^2 - 8x -1 =0
x^2 - 8x = 1
x^2 - 8x + (-4)^2 = 1 + (-4)^2
(x-4)^2 = 17
x-4 = ±√17
x = 4±√17
x = 4+√17 or x = 4-√17
x = 4+4.1231 or x = 4-4.1231
x= 8.1231 or x= -0.1231

Answer 5

use the quadratic formula which is

-b+/-sqrt(b^2-4ac)/2a (where A=1 B=-8 and C= -1)

U will have 2 answers which are x=8+sqrt68/2 and x=8-sqrt 68/2
so roughly X= 8.13 and x=-0.125