Completing the squre

Jackson332006

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Oct 19, 2006
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can someone tell me what I am doing wrong with this problem:

x^2 + 10x +13 = 0

x^2 +10x + 13 -13 = 0 - 13

x^2 + 10x = -13

x^2 + 10x + 25 = -13 + 25

(x + 5)^2 = 12

x + 5 = ±(sqrt)12
 
Jackson332006 said:
can someone tell me what I am doing wrong with this problem:

x^2 + 10x +13 = 0

x^2 +10x + 13 -13 = 0 - 13

x^2 + 10x = -13

x^2 + 10x + 25 = -13 + 25

(x + 5)^2 = 12

x + 5 = ±(sqrt)12

Everything looks fine so far. BUT, if you are to solve for x, you'll need to add -5 to both sides:

x = -5 + sqrt(12)

And, you're probably expected to simplify the radical. Since sqrt(12) can be thought of as sqrt(4*3), or sqrt(4)*sqrt(3), you can write that as 2 * sqrt(3).

x = -5 + 2 sqrt(3)

You've got two solutions:
x = -5 + 2 sqrt(3) OR x = -5 - 2 sqrt(3)
 
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