Răspuns:
Explicație pas cu pas:
Inmultim ec.2 cu 2:
1a)4x + 3y = 23
-4x + 2y = 32, le adunam:
0 +5y = 55, y =55/5 = 11
4x +3*11 = 23
4x = 23-33 = -10
x = -10/4, x = -5/2
b) Inmultim ec.1 cu -2:
-6x -22y = -28
6x -y = 5, le adunam:
0 +23y = -23, y =-1
6x +1 = 5
6x = 4, x = 4/6 = 2/3
2a) y = 7-2x
x -5(7-2x) = -13
x -35 +10x = -13
11x = 22, x = 22/11 = 2
y = 7-2*2, y = 3
etc
3. a+b =67 , a> b
a = 6c + 4
6c + 4 >= [67/2] >=34
6c > 30, c >= 5, c = 5,6,7,8,9
c = 5
a = 6*5+4, a = 34, b = 33
c=6
a = 6*6 +4, a =40, b = 27
etc
4. a+b = 20 |*-3
3a +5b =74
etc
