Răspuns :
fie x si y numerele necunoscute
x-y=28
x+y=490
x-y=28
x=28+y
x+y=490
28+y+y=490
2y=490-28
2y=462
y=462 impartit la 2
y=231
x=28+231
x=259
x-y=28
x+y=490
x-y=28
x=28+y
x+y=490
28+y+y=490
2y=490-28
2y=462
y=462 impartit la 2
y=231
x=28+231
x=259