ATTENTION - instead of a decimal comma should be used decimal DOT !
$ax^{2}+bx+c=0$

 a= b= c=

 $(x-x_{1})(x-x_{2})=0$ $x_{1,2}=\frac{-b\pm\sqrt{D}}{2a}=\frac{-b\pm \sqrt{(b^{2}-4ac)}}{2a}$ $D=b^{2}-4ac$