Posted by Marysvoice on Friday, February 15, 2008 at 7:31am.
What are the pros and cons of completing the square as a way to solve quadradic equations?

Algebra Quadratic Equations  Guido, Friday, February 15, 2008 at 8:02am
Completing the square is not the easiest way to solve quadratic equations; its strength lies in the fact that the process is repetitive and predictable.
Here is the best news: completing the square ALWAYS (SAY ALWAYS) will work, unlike the factoring method, which of course, requires that the trinomial be factorable.

Algebra Quadratic Equations  Marysvoice, Friday, February 15, 2008 at 9:28am
Thank you.

Algebra Quadratic Equations  drwls, Friday, February 15, 2008 at 8:15am
I find the quadratic equation
x = [b +/ sqrt(b^24ac)]/2a
the easiest to use, unless a way of factoring is obvious. It is derived by completing the square, after all. It tells you the number of real roots right away (from the value of b^2  4ac). The hard part is memorizing it, but after a while it becomes routine.

Algebra Quadratic Equations  Reiny, Friday, February 15, 2008 at 8:16am
I use the following rule:
If the coefficient of the squared term is 1 and the coefficient of the first degree term is even, then I would use completing the square, otherwise just use the quadratic formula
e.g.
x^2  12x 5 = 0
x^2  12x = 5
x^2  12x + 36 = 5 + 36
(x6)^2 = 31
x = 6 ± √31
In this case this method is actually faster and easier than using the formula, since the formula answer has to be broken down to lowest terms.

Algebra Quadratic Equations  Marysvoice, Friday, February 15, 2008 at 9:29am
Cool rule, thank you.
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