X+Y=5,2X+Y=8 .4X+3Y=5,X-2Y=4 .这2题用带如消元法解
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X+Y=5,2X+Y=8 .4X+3Y=5,X-2Y=4 .这2题用带如消元法解
7X-2Y=3,9X+2Y=-19 用加减消元法解
7X-2Y=3,9X+2Y=-19 用加减消元法解
1.代入消元法
x+y=5,y=5-x代入2x+y=8
2x+(5-x)=8解出x=3,y=5-x=2
x=3,y=2
由x-2y=4得x=4+2y代入4x+3y=5
4(4+2y)+3y=5,y=-1
y=-1代入x=4+2y=4-2=2
x=2,y=-1
2.加减消元:
两个式子相加,就削去了y
7x+9x=3-19
16x=-16
x=-1
代入其中任何一个可以算出y,y=-5
x=-1,y=-5
x+y=5,y=5-x代入2x+y=8
2x+(5-x)=8解出x=3,y=5-x=2
x=3,y=2
由x-2y=4得x=4+2y代入4x+3y=5
4(4+2y)+3y=5,y=-1
y=-1代入x=4+2y=4-2=2
x=2,y=-1
2.加减消元:
两个式子相加,就削去了y
7x+9x=3-19
16x=-16
x=-1
代入其中任何一个可以算出y,y=-5
x=-1,y=-5
3(x+y)-4(x-y)=11,2(x-y)+5(x+y)=27
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