Question 875488
here's the link that you showed me.
<a href = "http://gyazo.com/df24ccae44177730e6f7a41db326a995" target = "_blank">http://gyazo.com/df24ccae44177730e6f7a41db326a995</a>
here's the corrected solution:
<img src = "http://theo.x10hosting.com/2014/may1905.jpg" alt="$$$" </>


the standard form of the quadratic equation is ax^2 + bx + c
if you divide by a you get:
x^2 + (b/a)x + c/a = 0
you have to take 1/2 of the coefficient of the x term.
you will then get:
(x + b/2a)^2 - (b/2a)^2 + c = 0
the student didn't take half of the coefficient of the x term.
that was the student's first mistake.
then when the student took the square root of both sides of the equation, the student only took the positive side of the square root and not the negative side of the square root.
that was the second mistake.