Question

解下列方程组：

2s+3t=12 7m-3n=1 8x+3y+2=0
3s+4t=17 2n+3m=-2 4x+9=1-5y

Answer 1

2s+3t=12.....(1)
3s+4t=17.....(2)
(1)*4-(2)*3: 8s-9s=48-51
-s=-3
s=3
2*3+3t=12
3t=6
t=2

7m-3n=1....(1)
2n+3m=-2...(2)
(1)*2+(2)*3: 14m+9m=2-6
23m=-4
m=-4/23
2n+3*(-4/23)=-2
2n=-2+12/23
n=-17/23

8x+3y+2=0.....(1)
4x+9=1-5y.....(2)
由(2)： 4x+5y+8=0.....(3)
(1)-(2)*2： 3y-10y+2-16=0
-7y-14=0
y=-2
8x+3*(-2)+2=0
8x=4
x=1/2

Answer 2

2s+3t=123s+4t=178s+12t=489s+12t=51s=51-48=3t=(12-2s)/3=(12-2*3)/3=2 7m-3n=12n+3m=-214m-6n=29m+6n=-623m=-4m=-4/23n=(7m-1)/3=(7*(-4/23)-1)/3=-17/23 8x+3y+2=04x+9=1-5y8x+10y+18-2=8x+10y+16=07y+14=0y=-14/7=-2x=-(3y+2)/8=-(3*(-2)+2)/8=1/2

Answer 3

s=3 t=2 m=-4/17 n=-15/17 x=1/2 y=-2