Question

解下列方程组．(每小题5分，共30分)

(1)                           (2)

(3)                (4)

(5)                  (6)

Answer

(1) (2) (3) (4) (5) (6)

【解析】(1) 【解析】
将②代入①得

···································· 2分

将代入②得························· 4分

∴ 是原方程组的解··························· 5分

(2) 【解析】
①＋②得

···································· 2分

将代入①得

···································· 4分

∴ 是原方程组的解··························· 5分

(3) 【解析】
②－①得

···································· 2分

将代入①得

∴ 是原方程组的解··························· 5分

①

②

(4) 【解析】
原方程组变形为     ···················· 1分

由①得   ③

由②得    ④

③＋④得     x = 8··························· 3分

将x = 8代入④得 y = 1···························· 4分

∴是原方程组的解···························· 5分

(5) 【解析】
由①得

  ③································ 1分

由②得

 ④································ 2分

③×2得  ⑤

④×3得  ⑥

⑤－⑥得

····································· 3分

将y = 1代入④得

····································· 4分

∴ 是原方程组的解···························· 5分

(6) 【解析】
①＋②得

 ③·································· 1分

①－②得

 ④·································· 2分

③＋④得

····································· 3分

将代入③得y = – 2 ··························· 4分

∴ 是原方程组的解    5分