2x+y+3z=23,x+4y+5z=36,用含有z的代数式表示x
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2x+y+3z=23,x+4y+5z=36,用含有z的代数式表示x
2x+y+3z=23,x+4y+5z=36,用含有z的代数式表示x
2x+y+3z=23,x+4y+5z=36,用含有z的代数式表示x
消掉y就好了,第一式两边乘4,减第二式得
(8x+4y+12z)-(x+4y+5z)=23*4-36
所以7x+7z=92-36=56
x+z=8
x=8-z
因为2X+Y+3Z=23(此方程标记为①),X+4Y+5Z=36(此方程标记为②);
所以由①得2X=23-Y-3Z,
由②得X=36-4Y-5Z,
这两式想减得:2X-X=23-Y-3Z-(36-4Y-5Z)
因此:X=3Y+2Z-13 (此方程标记为③);
因为由①得:Y=23-2X-3Z,...
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因为2X+Y+3Z=23(此方程标记为①),X+4Y+5Z=36(此方程标记为②);
所以由①得2X=23-Y-3Z,
由②得X=36-4Y-5Z,
这两式想减得:2X-X=23-Y-3Z-(36-4Y-5Z)
因此:X=3Y+2Z-13 (此方程标记为③);
因为由①得:Y=23-2X-3Z,代入方程③得:
X=3(23-2X-3Z)+2Z-13
=69-6X-9Z+2Z-13
所以:X=8-Z
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2x+Y+3z=23,x+4y+5z=36,求X+2Y+3z~
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