解方程组4x+5y=3.5,x-1=1.8-x-6y

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解方程组4x+5y=3.5,x-1=1.8-x-6y
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解方程组4x+5y=3.5,x-1=1.8-x-6y
解方程组4x+5y=3.5,x-1=1.8-x-6y

解方程组4x+5y=3.5,x-1=1.8-x-6y
2式化成,2x = 2.8 - 6y,所以x = 1.4 - 3y
代入1式得,4(1.4 - 3y)+ 5y = 3.5
5.6 - 12y + 5y = 3.5
7y = 2.1
所以y = 0.3
带回去解得x = 0.5

4x+5y=3.5 (1)
x-1=1.8-x-6y
2x+6y=2.8 (2)
(2)×2-(1)
12y-5y=5.6-3.5
7y=2.1
所以y=0.3
x=(2.8-6y)/2=0.5

由x-1=1.8-x-6y 可得:x=1.4-3y,代入4x+5y=3.5得
4(1.4-3y)+5y=3.5
5.6-7y=3.5
7y=2.1
y=0.3
则x=1.4-3×0.3=0.5

x=0.5
y=0.3