1.{5x=7y-1 5x=17-14y 2.{x=16-4y y=34-4x 3.{x+y=7 x:5=y:2 4.{x+2y=1 x-4y=-22 5.{3x=y+1/2 3x=y/4

题目

1.{5x=7y-1 5x=17-14y 2.{x=16-4y y=34-4x 3.{x+y=7 x:5=y:2 4.{x+2y=1 x-4y=-22 5.{3x=y+1/2 3x=y/4

答案

1.5x=7y-1 ----(1)
5x=17-14y ----(2)
(1)*2+(2),15x=15,x=1.
5=7y-1,y=6/7.
2.x=16-4y ----(1)
y=34-4x ----(2)
(1)代入（2） y=34-4(16-4y),y=34-64+16y,y=2
x=16-8=8.
3.x+y=7 ----(1)
x:5=y:2 ----(2)
由(1)得 y=7-x,代入(2)得 x:5=(7-x):2,
2x=35-5x,7x=35,x=5;
y=7-x=2.
4.x+2y=1----(1)
x-4y=-22----(2)
(1)-(2),6y=23,y=23/6
x=1-2y=-20/3
5.3x=y+1/2 ----(1)
3x=y/4----(2)
(1)-(2),3y/4+1/2=0,y=-2/3
3x=y/4=-1/6,x=-1/18.