SOLUTION: Please solve using complete the square. My answer does not match the book: 2x^2+8x+1=0 2x^2+8x=-1 2(x^2+4x)=-1 2{(x^2+4x+(4/2)^2}=-1+2times(4/2)^2 2(x^2+4x+4)=7 2(x+2)^2=7 (

Question 221970: Please solve using complete the square. My answer does not match the book:
2x^2+8x+1=0
2x^2+8x=-1
2(x^2+4x)=-1
2{(x^2+4x+(4/2)^2}=-1+2times(4/2)^2
2(x^2+4x+4)=7
2(x+2)^2=7
(x+2)^2=7/2
x+2=+or-square root of 7/2
x=-2+or-square root of 7/2
The answer book states x=-2+or-the square root of 14/2
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!

You did the completion of the square correctly. The only problem you have is in the simplification of your answer.

You have:

Which IS a correct answer, it just isn't in simplest form. The problem is that the denominator of the fraction in the irrational part of the answer is irrational. You need to rationalize the denominator, thus:

Which I suspect matches your book's answer.

For more on this subject, see my lesson on rationalizing denominators:

http://www.algebra.com/algebra/homework/Radicals/rationalizingdenominators1.lesson

John

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