Question

三元一次方程!急死我了!1、x+y=2 y+z=-3 z+x=52、x+y=3 2x-3y-z=5 x-2y+z=-23

Answer 1

1.x+y=2 (1)

y+z=-3 (2)

z+x=5 (3)

(1)+(2)+(3):2(x+y+z)=4

x+y+z=2 (4)

(4)-(1):z=0

(4)-(2):x=5

(4)-(3):y=-3

2.x+y=3 (1)

2x-3y-z=5 (2)

x-2y+z=-2 (3)

(2)+(3):3x-5y=3 (4)

(1)*3:3x+3y=9 (5)

(5)-(4):8y=6

y=3/4

代y=3/4入(1):x+3/4=3

x=9/4

代x=9/4,y=3/4入(3):9/4 - 2*3/4 + z = -2

z=-11/4

(3) x+2y=3z (1)

3x-y=4z.(2)

(1)/(2):(x+2y)/(3x-y)=3/4

4(x+2y)=3(3x-y)

4x+8y=9x-3y

5x=11y

x:y = 11:5

4.类似题1的做法:

x+y=7 (1)

y+z=3 (2)

z+x-2=0 (3)

(3):z+x=2 (4)

(1)+(2)+(4):2(x+y+z)=12

x+y+z=6 (5)

(5)-(1):z=-1

(5)-(2):x=3

(5)-(4):y=4