ПОВТОРЮЄМО АЛГЕБРУ ЗА 7 КЛАС: 75

75. Розв’яжіть систему рівнянь:

1) 2a + 3b = 0; 4a + 6b = 0; 4a + 6b = 0; 4a + 6b = 0;

4a – 5b = –22; –4a + 5b = 22; 11b = 22; b = 2;

4a + 6 • 2 = 0; 4a + 12 = 0; 4a = –12; a = –3.

b = 2; b = 2; b = 2; b = 2.

2) 4x – 5y = 1; 8x – 10y = 2; 8x – 10y = 2; 8x – 10y = 2;

3x + 10y = 42; 3x + 10y = 42; 11x = 44; x = 4;

8 • 4 – 10y = 2; 32 – 10y = 2; 10y = 30; y = 3.

x = 4; x = 4; x = 4; x = 4.

3) 3x + 5y = 9; |• 3 9x + 15y = 27; 9x + 15y = 27;

4x – 3y = –17; |• 5 20x – 15y = –85; 29x = –58;

9x + 15y = 27; 9 • (–2) + 15y = 27; –18 + 15y = 27; 15y = 45;

x = –2; x = –2; x = –2; x = –2;

y = 3.

x = –2.