Question 327900: i am doing completing the square and i want to make sure i have it right
solve: x squared + 2x = 8 by completing the square
Found 3 solutions by stanbon, Earlsdon, meay7c:
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! solve: x squared + 2x = 8 by completing the square
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x^2 + 2x + 1 = 8 + 1
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(x+1)^2 = 9
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x+1 = +3 or x+1 = -3
x = 2 or x = -4
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Cheers,
Stan H.
Answer by Earlsdon(6294) (Show Source):
Answer by meay7c(10)  (Show Source):
You can put this solution on YOUR website! The problem : x^2 + 2x = 8, can be solved by completing the square as follows:
x^2 + 2x = 8
Next we want to take 1/2 of the coefficient, 2 which is 1 and then square 1.
1 squared is 1, so we add 1 to both sides:
x^2 + 2x + 1 = 8 + 1
Next we simplify:
x^2 + 2x + 1 = 9
Remember: x^2 + 2x + 1 is equivalent to (x + 1)^2. If we were to FOIL out
(x +1)^2 we would get: x^2 + 2x + 1.
In order to solve this equation, we will use (x + 1)^2 on the left hand side.
(x + 1)^2 = 9
To solve for x, we must undo the squaring operation on the left hand side. We do this by taking the square root of both sides:
sqrt(x + 1) ^2 = + or - sqrt (9)
Yielding: x + 1 = + or - 3
Next we evaluate:
x + 1 = 3 and x + 1 = -3
The first equation x + 1 = 3, x is 2.
The second equation x + 1 = -3, x = -4
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