(1)X+X+X+Y+Y=23(2)X+X+Y+Z=17(3)Z+Z+X+Y=15如题:列方程 求XYZ各等于多少
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(1)X+X+X+Y+Y=23(2)X+X+Y+Z=17(3)Z+Z+X+Y=15
如题:列方程 求XYZ各等于多少
3x+2y=23
2x+y+z=17 4x+2y+2z=34
x+y+2z=15
(4x+2y+2z)-(x+y+2z)=34-15
3x+y=19
(3x+2y)-(3x+y)=23-19
y=4
代入式子可得:x=5 y=4 z=3
(1)
x+y=5 ①
y+z=7 ②
z+x=6 ③
①-②
x-z=-2 ④
③+④
2x=4
x=2
代入④
2-z=-2
z=4
代入②
y+4=7
y=3
x=2 y=3 z=4
(2)
2x-2y+z=-9 ①
3x+2y-2...
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(1)
x+y=5 ①
y+z=7 ②
z+x=6 ③
①-②
x-z=-2 ④
③+④
2x=4
x=2
代入④
2-z=-2
z=4
代入②
y+4=7
y=3
x=2 y=3 z=4
(2)
2x-2y+z=-9 ①
3x+2y-2z=23 ②
x+y+z=12 ③
①+②
5x-z=14
z=5x-14 ④
①+③*2
4x+3z=15
将④代入
4x+3(5x-14)=15
4x+15x-42=15
19x=57
x=3④
代入④
z=1
x=3 z=1代入③
3+y+1=12
y=8
x=3 y=8 z=1
(3)
37x+43y=203 ①
43x+37y=197 ②
①-②
-6x+6y=6
y=1+x
代入①
37x+43(1+x)=203
80x=160
x=2
y=3
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