解下列方程组.(每小题5分,共30分)(1)(2)(3)(4)(5)(6)-七年级数学

题文

解下列方程组.(每小题5分,共30分)
(1)                           (2)
(3)                (4)
(5)                  (6)

题型:解答题  难度:偏易

答案

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

(1) 解:将②代入①得


···································· 2分
代入②得························· 4分
是原方程组的解··························· 5分
(2) 解:①+②得
···································· 2分
代入①得

···································· 4分
是原方程组的解··························· 5分
(3) 解:②-①得

···································· 2分
代入①得


是原方程组的解··························· 5分



 
(4) 解:原方程组变形为     ···················· 1分

由①得   ③
由②得    ④
③+④得     x =" 8···························" 3分
x = 8代入④得 y =" 1····························" 4分
是原方程组的解···························· 5分
(5) 解: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
y = 1代入④得
····································· 4分
是原方程组的解···························· 5分
(6) 解:①+②得
 ③·································· 1分
①-②得