用代入法做方程 1.{2x-y=8 ① x+3y=-3 ② 2.{2x-3y=1 ① 3x+2y=8 ②3.{(x+y)/2-(x-y)/6=1 ① 3x+4y=0 ②4.{(x+y)/2+(x-y)/3=6 ① 4(x+y)-5(x-y)=2 ②尽快 ..求你们了
用代入法做方程 1.{2x-y=8 ① x+3y=-3 ② 2.{2x-3y=1 ① 3x+2y=8 ②
3.{(x+y)/2-(x-y)/6=1 ① 3x+4y=0 ②
4.{(x+y)/2+(x-y)/3=6 ① 4(x+y)-5(x-y)=2 ②
尽快 ..求你们了
1,因为2x-y=8 ,所以y=2x-8
把y=2x-8带入x+3y=-3中,则x+3(2x-8)=-3
化简得x=2.1 , y=2x-8=2x2.1-8=-3.9
2.因为x+2y=8 ,所以x=8-2y
把x=8-2y带入2x-3y=1中,则y=15/7 所以x=8-2y=26/7
3.将①化简得x+2y=3,所以x=3-2y将其带入②,化简得y=9/2
把y=9/2带入x=3-2y,则x=-6
4.将②化简得x=9y-2,将其带入①,化简得y=1
将y=1带入x=9y-2,则x=7
1、3*① + ② = 3* 8 - 3 = 21 ---> 6x - 3y + x + 3y = 21 -----> 7x = 21 ----> x = 21 / 7 = 3
由①可得:y = 2x - 8 = 2 * 3 - 8 = 6 - 8 = -2
2、2*① + 3*② = 2 * 1 + 3 * 8 = 2 + 24 = 26 -----> 4x - 6y + 9x + 6y = 26 ----> 13x = 26 --> x = 2
由①可得:3y = 2x - 1 ---> 3y = 3 ---> y = 1
3、6*① = 1 * 6 = 6 -----> 3(x+y) - (x-y) = 6 ---> 3x + 3y - x + y = 2x +4y = 6
--->同除2 ---> x + 2y = 3 ③
2③ - ② = 2 * 3 - 0 = 6 ----->2(x + 2y) - (3x + 4y) = 6 ---> 2x + 4y - 3x - 4y = 6 ---->
-x = 6 -----> x = -6 由③可得:2y = 3 -x =3 + 6 = 9 -----y = 9 / 2 = 4.5
4、6*① = 6 * 6 = 36 ----> 3(x + y) + 2(x - y) = 36 ----> 3x + 3y + 2x -2y = 5x + y = 36 ③
由②可得:4x + 4y - 5x + 5y = 2 ----> -x + 9y = 2 ④ ---> ③ + 5④ = 36 + 5 * 2 = 46 ---->
5x + y - 5x + 45y = 46 ---->46y = 46 ---> y = 1
由④可得:x = 9y - 2 = 9 - 2 = 7
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由①得到Y=2X-8……③
将③ 代入②得到X+3(2X-8)=-3
7X=-3+24
X=3
将X=3代入③得到Y=-2
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由①得到Y=(2X-1)/3……③
将③ 代入②得到3X+2((2X-1)/3)=8
13X-2=24
X=2
将X=2代入③得到Y=1
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由②得到X=-4Y/3……③
将③ 代入① 得到(-4Y/3+Y)/2-(-4Y/3-Y)/6=1
-Y+7Y/3=6
Y=9/2
将Y=9/2代入③得到X=-6
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(x+y)/2+(x-y)/3=6 ① 4(x+y)-5(x-y)=2 ②
由②得到X=9Y-2……③将③ 代入① 得到(9Y-2+Y)/2+(9Y-2-Y)/3=6
Y=1
将Y=1代入③得到X=7
1.一式算出y=2x-8然后带入二式。
得x 6x-24=-3
7x=21
x=3 y=-2
2题。一式乘以3..二式乘以2
得6x-9y=3......6x 4y=16
一式求出6x=3 9y带入二式
得13y=13
y=1 x=2
3题一式先通分再相减得2x 2y=6
一式再乘以2然后解出4y=12-4x
带入二式得x=12 y=-9
4题x=7 y=-1
由1得-y=8-2x y=-8+2x ③
将③带入②得x+3(-8+2x)=-3
解得7x=21
x=3
将其代入③得y=-2