1≤i≤n,1≤j≤m olsun.
n∑i=1m∑j=1aij
=m∑j=1a1j+m∑j=1a2j+m∑j=1a3j+...+m∑j=1anj⏟n
=(a11+a12+a13+...+a1m)⏟m+(a21+a22+a23+...+a2m)⏟m+(a31+a32+a33+...+a3m)⏟m+...+(an1+an2+an3+...+anm)⏟m
=(a11+a21+a31+...+an1)⏟n+(a12+a22+a32+...+an2)⏟n+(a13+a23+a33+...+an3)⏟n+...+(a1n+a2n+a3n+...+amn)⏟n⏟m
=n∑i=1a1i+n∑i=1a2i+n∑i=1a3i+...+n∑i=1ami⏟m
=m∑j=1n∑i=1aji