聯立方程` f2程度 =]

2007-04-13 7:25 pm

用代入法法解而2條聯立方程呀`
1) 2x+3y=5......................(1)
x-y=5..........................(2)

2) 4x+3y=8.....................(1)
3x-y=6......................(2)

唔該晒` -,- 好急的
16號要交 t^t

更新1:

咁用加減消元法解方程- 1) x-y=2...........(1) x+y=5..........(2) 2) 4x+3y=10..................(1) 2x-4y=5....................(2)

更新2:

下面呢2條就咁解聯立方程就得` *3* 1) 8x+3y=24...............(1) 5x+2y=14...............(2) 2) 6x+3y-5=0 ..........(1) 4x+5y-3=0...........(2)

更新3:

仲有呀.... s0rry 3) x + y =1 ─ ─ 3 4 x - y = 1 — — — 5 10 2 4) x-y+4=0 3x-16y-1=0

更新4:

仲有係其他數: 1) 兩數之和是24 ,大數比小數多3,求小數。 2) 在農場中養有雞和兔。若牠們合共有20個頭及50隻腳,求雞的數目。 3) 6公斤普洱與10公斤香片混合,總值$120。若35公斤普洱的價值與25公斤香片的價值相等,求5公斤普洱的價值。唔該晒` 係咁多了 t3t

回答 (5)

John

2007-04-13 7:31 pm

✔ 最佳答案

1)

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

x-y=5............... ...........(2)

From (2),

x = 5 + y ---(3)

sub. (3) into ( 1 )

2(5 + y) + 3y = 5

10 + 5y = 5

5y = -5

y = -1

sub. into (3)

x + 1 = 5

x = 4

2)

From (2),

y = 3x - 6 ---(3)

sub. (3) into (1)

4x + 3 (3x - 6) = 8

13x - 18 = 8

13x = 26

x = 2

sub. into (3)

y = 3x - 6

y = 6 - 6

y = 0

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[匿名]

2007-04-13 7:43 pm

1)
2x+3y=5.........(1)
x－y=5..............(2)
x=5－y.......(3)
(1) 2(5－y)+3y=5
10－2y+3y=5
y=5－10
y=－5
代y=－5入(3)
x=5-(-5)
x=5+5
x=10
∴y=-5,x=10
-------------------------------------
2) 4x+3y=8.........(1)
3x-y=6............(2)
唔係好識．．．ｓｏｒｒｙ呀...

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Chun Yin

2007-04-13 7:39 pm

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

Subs. (1) into (2)
(5-3y)/2-y=5
y= -1
Subs. y= -1 into (1)
2x+3y=5
2x+3*-1=5
x=4

2. 4x+3y=8...........(1)
3x-y=6...........(2)
(1) x=(8-3y)/4
Subs. x=(8-3y)/4 into (2)

3((8-3y)/4)-y=6
y=0
Subs. y=0 into(1)
4x+3*0=8
x=2

以上是伐入法,但我覺得消元法(elimination)較好用.......

參考: 我

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維維

2007-04-13 7:36 pm

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

(2)x=5-y...(3)

代(3)入(1)

2(5-y)+3y=5

10-2y+3y=5

-2y+3y=5-10

y=-5

代y=-5入(2)

x-(-5)=5

x+5=5

x=0

x=0,y=-5

2) 4x+3y=8.....................(1)
3x-y=6......................(2)

(2):-y=6-3x

y=3x-6....(3)

代(3)入(1)

4x+3(3x-6)=8

4x+9x-18=8

13x=8+18

x=2

代x=2入(2)

3(2)-y=6

6-y=6

y=0

x=2,y=0

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用戶138786

2007-04-13 7:32 pm

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

將y=-1代入(2)

x-(-1)=5
x=4

所以x=4, y=-1

4x+3y=8.....................(1)
3x-y=6......................(2)
-------------------------------------
(2)*3 9x-3y=18.............(3)
-----------------------------------
(1)+(3) 13x=26
x=2

將x=2代入(1)

4(2)+3y=8
y=0

所以x=2, y=0

參考: 自己

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