\documentclass[11pt,a4paper,twoside]{article}
\usepackage[a4paper,top=2.5cm,bottom=2cm,left=2.5cm,right=2.5cm]{geometry}
\usepackage{amsmath,amssymb,dsfont}
\documentclass[11pt,a4paper,twoside]{article}
\usepackage[a4paper,top=2.5cm,bottom=2cm,left=2.5cm,right=2.5cm]{geometry}
\usepackage{amsmath,amssymb,dsfont}