Question

4x+-z=12 3x+2y+z=-5 x-y+5z=1 三元一次方程答案急需！！！！！！！！！！！！！！

Answer 1

题目有误，应该是
4x+y-z=12 (1)
3x+2y+z=-5 (2)
x-y+5z=1 (3)
(1)+(2)，得 7x+3y=7 , y=7/3(1-x) (4)
(2)×5-(3)，得 14x+11y=--26 (5)
把（4）代入（5）得
14x+77/3(1-x)=-26
42x+77-77x=-78 35x=155
x=31/7 代入（4）得
y=7/3(1-31/7)=7/3×(-24/7)=-8
把x=31/7 ,y=-8 代入（1）得
124/7-8-z=12
z=124/7-8-12=124/7-140/7=-16/7
∴ x=31/7 y=-8, z=-16/7

Answer 2

4x+-z=12 (1)
3x+2y+z=-5 (2)
x-y+5z=1 (3)
(2) + 2(3)
5x+11z =-3 (4)
(4) +11(1)
49x = 129
x = 129/49
from (1)
z = -459/49
from (3)
x-y+5z=1
129/49 -y -2295/49 =1
y =-2215/49