documentclass[11pt,a4paper]{article}
    usepackage{blindtext}
    usepackage{mathtools}
    DeclareMathOperator{sgn}{sgn}
begin{document}
begin{flalign*}
&+(+a)=+a,& &-(+a)=-a&\
&+(-a)=-a,& &-(-a)=+a&
end{flalign*}
end{document}