《消元——解二元一次方程组》第三课时练习题(含答案).docx

8.2元元一一解二元一次方程组（3）1 .二元一次方程组；x+y=10的解是。2x-y = -12.x+2y =m的解满足x-y=5,则m的值为2x y =13.若关于x、y的二元一次方程组Zx + y = 5 x-2y =1ax by = 3 有相同的解，则ax - by = 1a=5.若，x = 1、 一.x 1是方程组y =2ax by =的解，则a、b的值为（bx - ay = 36.A.a =1b =2B.a = -1b = 2C.a =1D. b = 1a = -2b - -1在3x-5y = 22x-3t =4(3)y = x -23x-y = 124x-3y = 23x-4y= -2、b= o4.若3x5""y2与5x6y3a/b是同类项，则a=中,x - 2x 2的有(y =2A.7.(1)和(3) B.(2)对于方程组:4x+7y=-194x -5y =17和(3)C.,用加减法消去A. 2y= -2 B. 2y=36 C. 12y=8.(1)和(4)D. (2)和(4)x,得到的方程是（-2D. 12y=36一 、一11将方程1x+y=1中x的系数变为5,则以下正确的是（ 2A. 5x+y=7 B. 5x+10y=10 C. 5x9.用加减法解下列方程组10y=10 D. 5x -10y=-10/八3m 2n =5(1)4m +2n =9(2)；3x-5y = 7、4x + 2y = 56x -5y =11-4x-4y =771x9y =124x +3y = 5(5)52 y=50.5x -0.3y =0.25x + 2y = 5a,"上 比必.、,(其中a为常数)3x + 4y = 3a10.用加减消元法解方程组4x+3y =3、3x + 5y = -67x + 4y = 23x-6y = 242x +5y =5、3x5y =103x + 2y = 5、2x + 5y = 711.甲、乙两人同解方程组3LAx + By = 2e 十小丘”日y 。甲正确解得1、Cx _ 3 y = _2x = 1x 1 、乙因抄错C,、y = -1解得二2,求：A、B、C的值。-612.已知：2x+5y+4z=15, 7x+y+3z=14;求：4x+y+2z 的佰。参考答案1.2. m= 4y =73. a=2 b=14. a=1 , b=05. D6. C7. D8. D9.3 x =217 = "23x =161y =-2214 x =1712 y =1710.(1)解：x 4一x 3得：11y=33y= 3把y= 3代入得：4x 9=3x=3原方程组解为/y = -3(2)解：X 3+X 2 得：27x=54x=2把x=2代入得：4y=-12y= -3x = 2原方程组解为:J = -3(3)解：+得：5x=15x=3把x=3代入得：5y= - 1x =3：原方程组解为1ly = -5(4)解：X 3X 2 得：11y=11y=1把y=1代入得：3x=3x=1原方程组解为x =1y = 111.解：由题意得:Ax+By = 2 y 的解，Cx 3y = 2x =22是方程y - - 6Ax + By =2 的解;x = 1把 J 1y = 1二2 ,代入Ax + By = 2得:=-6A-B =22A6B =2aT解关于A B的方程组得:2B2x =1 一一一把 代入Cx3y = 2得：C=- 5J = -15 _ 1一 , .A = B = C - -5 22s Q5y+4z = 15-2x(1)12.解：3，、y+3z=14-7x(2)(2) X5 (1)得：11z=55 -33x. z=53x(3)把(3)代入(2)得：y= 1+2x把 y= 1+2x z=5 - 3x 代入 4x+y+2z 得：4x 1+2x+10 6x=9