Pt. primul sistem: {2x+y=8; 2x-3y=-8}, a doua ecuatie o inmultim cu -1 => {2x+y=8; -2x+3y=8}, le adunam => 4y=16 => y=4; 2x+4=8 <=> 2x=4 => x=2. Pt. al doilea sistem: {13x-7y=6; 7x+13y=20}, inmultim prima ec. cu -7, iar a doua cu 13 => {-91x+49y=-42; 91x+169y=260}, le adunam => 218y=218 => y=1; 13x-7=6 <=> 13x=13 => x=1.
