{超急!!} 數學數學數學(10分)

2010-09-29 1:27 am
★利用加減消元法解下列聯立二元一方程。

1). x+y=8......(1)
x-y=2......(2)

2). m-n=2......(1)
m+n=-2......(2)


3). x+3y=5......(1)
x+2y=3......(2)

4). 5m+2n=8......(1)
3m-2n=8......(2)

5). 2x-7y=9......(1)
2x+3y=19......(2)

6). 4x-3y=2......(1)
-3y+x=5......(2)

7). x+y=4......(1)
2x+3y=10......(2)

8). 3x-5y=5......(1)
x+3y=3......(2)

9). 2x-y=3......(1)
5x-3y=4......(2)

10). x-3y=1.....(1)
5x+y=5......(2)

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回答 (2)

2010-09-29 2:03 am
✔ 最佳答案
1)x+y=8....(1)
  x-y=2....(2)
解︰
(2)-(1),x-y-x-y=2-8
            -2y=-6
              y=3
把y=3代入(1)
x+3=8
  x=5



2)m-n=2....(1)
  m+n=-2...(2)
解︰
(2)-(1),m+n-m+n=-2-2
             2n=-4
              n=-2
把n=-2代入(1)
m+2=2
  m=0


3)x+3y=5......(1)
  x+2y=3......(2)
解︰
(2)-(1),x+3y-x-2y=5-3
                y=2
把y=2代入(1)
x+3(2)=5
     x=-1

4). 5m+2n=8......(1)
  3m-2n=8......(2)
解︰
(2)+(1),5m+2n+3m-2n=8+8
                 8m=16
                  m=2
把m=2代入(1)
5(2)+2n=8
      n=-1



5). 2x-7y=9......(1)
 2x+3y=19......(2)
解︰
(2)-(1),2x-7y-2x-3y=9-19
               -10y=-10
                  y=1
把y=1代入(1)
2x-7(1)=9
      x=8 


6). 4x-3y=2......(1)
 -3y+x=5......(2)
解︰
(2)-(1),4x-3y+3y-x=2-5
                3x=-3
                 x=-1
把x=-1代入(1)
4(-1)-3y=2
       y=-2

7-10就自己慢慢解吧!我累了
我不喜歡用電腦做數,那樣很容易累…
7-10解的方式是一樣的
2010-09-29 4:58 am
7). x+y=4......(1)
2x+3y=10......(2)
_________________
(1)x2:
2x+2y=8--------------(3)

(2)-(3):
y=2

Put y=2 into 1:
x=2

2010-09-28 21:05:52 補充:
3x-5y=5......(1)
x+3y=3......(2)
______________
From2:
x=3-3y---------3

Sub. 3 into 2:
3(3-3y)-5y=5
-14y.........=-4
y..............=2/7

Put y=2/7 into 3:
x=15/7

2010-09-28 21:08:15 補充:
9). 2x-y=3......(1)
5x-3y=4......(2)
_______________
From1:
y=2x-3--------------3

Sub. 3 into 2:
5x-3(2x-3)=4
-x............=-5
x=5

Put x=5 into 3:
y=7

2010-09-28 21:09:40 補充:
10). x-3y=1.....(1)
5x+y=5......(2)
_____________
From1:
x=3y+1------------3

Sub. 3 into 2:
5(3y+1)+y=5
16y..........=0
y=0

Put y=0 into 3:
x=1
____________


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