The equation [tex]ax^2+bx+c=0[/tex] has solutions given by [tex]x=\frac{-b \pm \sqrt{b^2-4ac}}{2a}[/tex]. This means take the numbers a, b and c then plug them into that formula on your calculator and bam, answers.
The [tex]b^2-4ac[/tex] bit is called the discriminant and it tells you what kind of solutions occur,
-if [tex]b^2-4ac \ \textgreater \ 0[/tex] then the equation has two different solutions
-if [tex]b^2-4ac=0[/tex] then the equation has exactly one solution
-if [tex]b^2-4ac\ \textless \ 0[/tex] then the equation has no (real) solutions.
So you are interested in exactly one solution which happens if [tex]b^2-4ac=0[/tex] or equivalently [tex]b^2=4ac[/tex].
