documentclass[a4paper]{article}

usepackage{mathtools}
usepackage{lipsum}

begin{document}

lipsum*[2]

begin{equation}
  begin{multlined}[.7textwidth]
    shoveleft{a = b + }\
    shoveright{+ c}
  end{multlined}
end{equation}

lipsum*[2]

end{document}