## beth12345 4 years ago how to find the value of 'X' when x^2-8x=8?

1. Mimi_x3

$x^2-8x-8 = 0$ Use the quadratic formula: $\frac{-(b)\pm\sqrt{(b)^{2}-4(a)(c)}}{2(a)}$ $a = 1 , b=-8 , c = -8$ And sub it in.

2. beth12345

ok thanx

3. anonymous

use the quadratic formula. $(-b \pm \sqrt{b ^{2} -4ac}) /2a$

4. anonymous

x^2-8x=8 x(x-8)=8 or x=2 and x-8=4 x=2, x=12

5. beth12345

thank you, i never thouht of it that way but i can see how it works :)

6. anonymous

but this solution is wrong

7. beth12345

?

8. anonymous

x=2, x=12 is a wrong solution

9. Mimi_x3

Completing the square would work as well. But using the quadratic formula is easier.

10. beth12345

i thought it would be like (2)[(12)-8]=8?

11. beth12345

oh ok, mimi, i did the formula and got 4+or-2root6, is that right?

12. anonymous

Ravi, in case you were wondering why it's wrong it's because you must factorise the equation equal to 0. 8 has an infinite number of non-integer factors, so you can't solve. 0, on the other hand, must have the value of a factor as 0.

13. beth12345

thanks samarilli, i see now why it's not the same answer as when i use the formula

14. Mimi_x3

Well, i got $\frac{-8\pm\sqrt{96}}{2}$

15. anonymous

thanks Simarilli