Question

用代入法解下列方程组(急用,答完再给50分)

Answer 1

1.

y=x+3.(1)

7x+5y=9.(2)

解(1)代入(2),

7x+5(x+3)=9

7x+5x+15=9

解得,

x=-1/2

y=(-1/2)+3=5/2

2.

3s-t=5.(1)

5s+2t=15.(2)

(1)*2+(2)得,

11s=25,t=25/11

将t=25/11代入(1)

3s-25/11=5

s=(5-25/11)/3=10/11

3.

3x+4y=16.(1)

5x-6y=33.(2)

(1)*3+(2)*2得,

19x=16*3+33*2=114

x=114/19=6

将x=6代入(1),

3*6+4y=16

y=-1/2

4.

4(x-y-1)=3(1-y)-2.(1)

x/2+y/3=2.(2)

整理(1)得,

4x-y=5.(3)

整理(2)得,

3x+2y=12.(4)

(3)*2+(4)得,

11x=22,x=2

将x=2代入(3),

4*2-y=5,y=3