Question

Solve by completing the square..

Answer 1

\[2x^2 + 4x - 11 = 0\] I know already that I have to use this formula to complete it: \[[\frac{ 1 }{ 2 }(b)]^2\] but my answers are not working out for factoring. Any help is appreciated :)

Answer 2

I'm not sure how they teach this problem, but perhaps it will be okay to show you how I solve it.

You need \[(2x+u)(x-v)\] to get \[2x^2+4x+uv\]

Cross multiplying the first equation and comparing the x terms from both equations gives:
\[4x = xu - 2xv\\ 4 = u - 2v\] There is an entire line of answers to the above equation of course, but using \[v=1\] gives \[u = 6\]

So,
\[(2x+6)(x-1) = 2x^2+4x-6\] and if we subtract five from that we have your original equation...