SOLUTION: The problem: 2x^2 - 12x - 7 = 0
the directions are to solve by completing the square.
This is what I did:
2x^2 - 12x = 7
2x^2 - 12x + 36 = 43
2(x(x-6) + 18) = 43
x(x-6)+ 18 =
Question 771122: The problem: 2x^2 - 12x - 7 = 0
the directions are to solve by completing the square.
This is what I did:
2x^2 - 12x = 7
2x^2 - 12x + 36 = 43
2(x(x-6) + 18) = 43
x(x-6)+ 18 = (43/2)
x(x-6) = (7/2)
x^2 - 6x = (7/2)
I keep getting stuck
I know that the answers are 6.5355 and -.5355 from plugging it into the quadratic formula, but I don't know how to get there by completing the square.
Thank you so much for any help Answer by Edwin McCravy(20055) (Show Source):
2x² - 12x = 7
You didn't divide through by the coefficient of x².
You must do that first:
=
x² - 6x =
Half of -6 is -3. Square -3, (-3)² = 9, Add 9 to both sides:
x² - 6x + 9 = + 9
(x-3)(x-3) =
(x - 3)² =
√(x - 3)² =
x - 3 =
x - 3 =
x - 3 =
x - 3 =
x - 3 =
x = 3 ±
x = ±
x =
That's the correct answer.
2x^2 - 12x = 7
2x^2 - 12x + 36 = 43 <--- forgot to divide through by 2
2(x(x-6) + 18) = 43 <--- shouldn't factor x out of the first two terms
x(x-6)+ 18 = (43/2)
x(x-6) = (7/2)
x^2 - 6x = (7/2)
