SOLUTION: Solve by completing the square. 2x^2-12x-18=0 How do you do it. Thanks

Question 66792: Solve by completing the square.
2x^2-12x-18=0
How do you do it. Thanks
Found 2 solutions by Earlsdon, ptaylor:
Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
Solve by completing the square:
First, you want to get the coefficient of the term to be 1, so divide everything by 2.
Simplify.
Now move the constant term (-9) to the right side of the equation by adding 9 to both sides.
Next, add the square of half the x-coefficient = 9 to both sides.
Now factor the left side.
Take the square root of both sides.
= +/- Add 3 to both sides.
Simplify. Note that: =

Answer by ptaylor(2198) (Show Source): You can put this solution on YOUR website!
Solve by completing the square.
2x^2-12x-18=0
How do you do it. Thanks
2x^2-12x-18=0 This is in standard form with A=2, B=-12 and C=-18.
First, divide each term by 2; (we want A to equal 1) and we get:
x^2-6x-9=0 now add 9 to both sides (we are setting up the left side so we can complete the square) and we have:
x^2-6x+9-9=9
x^2-6x=9 Now we will complete the square on the left side. In other words, we will select a C for the left side that results in the left side being a perfect square. When A=1, we can take half B , square it, and add it to both sides. We will now have a perfect square on the left side. Another way to look at it is: when A=1, then B is the sum of the factors of C. Here, we are choosing the factors of C that results in a perfect square and this will work in most every case.
(1/2)B=-3 squaring it, we get 9. So we add 9 to both sides
x^2-6x+9=18
(x-3)^2=18 take the square root of both sides
x-3=+or-sqrt(18)=+or-sqrt(9)(2)
x=3+3sqrt(2)=3(1+sqrt(2))
x=3-3sqrt(2)=3(1-sqrt(2))
Ck by using the quadratic formula
Hope this helps---ptaylor

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