3x+2y-4z=9,(1) 3x+5y-5z=14(2) 3x-4y+2z=3(3)
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3x+2y-4z=9,(1) 3x+5y-5z=14(2) 3x-4y+2z=3(3)
3x+2y-4z=9,(1)
3x+5y-5z=14(2)
3x-4y+2z=3(3)
适合用( 可用(2)-( ),(3)-( ),得到一个含y,z的二元一次方程组.
3x+2y-4z=9,(1)
3x+5y-5z=14(2)
3x-4y+2z=3(3)
适合用( 可用(2)-( ),(3)-( ),得到一个含y,z的二元一次方程组.
3x+2y-4z=9,(1)
3x+5y-5z=14 (2)
3x-4y+2z=3 (3)
解(2)-(1)得:3y -z = 5 (4)
(2) - (3) 得 :9y -7z = 11 (5)
(4)×3 -(5)得:4z = 4 解得:z = 7
把z=7代入(4)得 3y = 5 + z,y = (5+z)/3 = (5+7)/3 = 4
把 y = 4,z = 7 代入(1)得 3x = 9 - 2y + 4z
x = (9-2y+4z)/3 = (9 - 2×4 + 4×7)/3 = 29/3
所以三元一次方程组的解是:x = 29/3,y = 4,z = 7
3x+5y-5z=14 (2)
3x-4y+2z=3 (3)
解(2)-(1)得:3y -z = 5 (4)
(2) - (3) 得 :9y -7z = 11 (5)
(4)×3 -(5)得:4z = 4 解得:z = 7
把z=7代入(4)得 3y = 5 + z,y = (5+z)/3 = (5+7)/3 = 4
把 y = 4,z = 7 代入(1)得 3x = 9 - 2y + 4z
x = (9-2y+4z)/3 = (9 - 2×4 + 4×7)/3 = 29/3
所以三元一次方程组的解是:x = 29/3,y = 4,z = 7
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