[tex]y=a x^{2} +bx+c[/tex]
[tex]y= x^{2} +bx[/tex]
[tex]y=a x^{2} +c[/tex]
Where a,b,c are real numbers and a[tex] \neq [/tex] 0.
Just remember that quadratic equation always has the [tex] x^{2} [/tex].
Example:
(x-2)(x+2) = [tex] x^{2} -4[/tex]
(x+2)(x+2)=[tex] x^{2} +4x+4[/tex]
2x(x+2)=[tex]2 x^{2} +4[/tex]
I hope that helps... :)