how to find the value of 'X' when x^2-8x=8?

Question

mimi_x3 · Answer

$$x^2-8x-8 = 0 $$
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.

beth12345 · Answer

ok thanx

anonymous · Answer

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

anonymous · Answer

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

beth12345 · Answer

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

anonymous · Answer

but this solution is wrong

beth12345 · Answer

?

anonymous · Answer

x=2, x=12 is a wrong solution

mimi_x3 · Answer

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

beth12345 · Answer

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

beth12345 · Answer

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

anonymous · Answer

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.

beth12345 · Answer

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

mimi_x3 · Answer

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

anonymous · Answer

thanks Simarilli