Question 7474: How to solve this quadratic equation by completing the square
x^2 + 6X - 7 = 0
Answer by longjonsilver(2297)   (Show Source):
You can put this solution on YOUR website! ok, completing the square...
 . First ignore the 7. Just think about the  . What i want to do is think of the correct number (not the 7) that needs to be there so that I can factorise the quadratic as  where k is a "nice" number, usually an integer, sometimes a simple fraction, rarely a horrible number.
think about . This expands to be  , so we look at the coefficient before the x-term, our +6, and we note that this is like the "2k", so k must be 3. The number we therefore require  is +9, so what we need is:
 .
That is it done, really. All we have to do now is get this to look like the original, , as follows:
 ...note the +9-9 cancel each other out, leaving the -7
Hope this is clear?
And now to answer the question... 
 or 
so x+3 = 4 OR x+3 = -4
so x=1 OR x=-7
jon.
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