Quadratic equation

ATTENTION - instead of a decimal comma should be used decimal DOT !

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