这道数学题怎么做 x+y+2z=7 x-2y-z=-4 2x+3y+z=18
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x+y+2z=7--------(1)
x-2y-z=-4--------(2)
2x+3y+z=18-----(3)
(1)×2得:2x+2y+4z=14------(4)
(2)×2得:2x-4y-2z=-8--------(5)
(4)-(5)得:6y+6z=22 化简得:3y+3z=11-----(6)
(3)-(5)得:7y+3z=26 -----(7)
(7)-(6)得:4y=15,即:y=15/4
将y=15/4代入(6):3×15/4+3z=11,解得:z=-1/12
将y=15/4 z=-1/12代入(1):x+15/4+2×(-1/12)=7,解得:x=41/12
即此题解为:x=41/12 y=15/4 z=-1/12
x-2y-z=-4--------(2)
2x+3y+z=18-----(3)
(1)×2得:2x+2y+4z=14------(4)
(2)×2得:2x-4y-2z=-8--------(5)
(4)-(5)得:6y+6z=22 化简得:3y+3z=11-----(6)
(3)-(5)得:7y+3z=26 -----(7)
(7)-(6)得:4y=15,即:y=15/4
将y=15/4代入(6):3×15/4+3z=11,解得:z=-1/12
将y=15/4 z=-1/12代入(1):x+15/4+2×(-1/12)=7,解得:x=41/12
即此题解为:x=41/12 y=15/4 z=-1/12
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