3x + 5 = 8y + 4 = 7(x+y) -1步驟

3x+5=8y+4---------(1)
8y+4=7(x+y)
8y+4=7x+7y
y=7x-4-----------(2)
Put (2) into(1)
3x+5=8(7x-4)+4
3x+5=56x-32+4
33=53x
x=33/53
putx=33/53 into (2)
y=7(33/53)-4

3x+5=8y+4=7(x+y)-1
The above equations can be written as
3x+5=7(x+y)-1------------------(1)
{ 8y+4=7(x+y)-1------------------(2)

From (1),3x+5=7x+7y-1
-4x-7y=-6--------------(3)
From (2),8y+4=7x+7y-1
-7x+y=-5---------------(4)
(4)*7, -49x+7y=-35------------(5)
(3)+(5), -53x=-41
x=41/53
Sub.x=41/53 into(3)
-4(41/53)-7y=-6
-164/53-7y=-6
-7y=10/53
y=-10/371

對不起﹐學校對我來說已是很久的事﹐但也讓我試試看吧。

從你提供的方程式﹐我們可以分出 3 條方程式﹕
1) 3x+5 = 8y+4
2) 3x+5 = 7(x+y)-1
3) 8y+4 = 7(x+y)-1

(1) 可變成 y = (3x+1)/8
(2) 可變成 y = (-4x+6)/7

(1) = (2) => (3x+1)/8 = (-4x+6)/7
稱這方程式為 (4)

(4) 可變成 x = 41/53

把 (4) 代入 (1) 或 (2) 或 (3) 隨便 1 條﹐可得出 y 的值。
自己試試看吧﹐祝成功﹗

3X+5= 8Y+4= 7X+7Y-1
所以Y=7X-5
3X+5=8Y+4
3X+5=8(7X-5)+4
3X+5=56X-36
41=53X
53/41=X

Y=7X(53/41)-5
Y=166/41

= ="怪怪地"

2007-12-16 13:27:20 補充：
唔似小學數^^"

3x + 5 = 8y + 4 = 7(x+y) -1
3x + 5 = 8y + 4.......................(a)
8y + 4 = 7(x+y) -1...................(b)

(a) 3x + 5 = 8y + 4
3x = 8y + 4 - 5
x = (8y -1) / 3

(b) 8y + 4 = 7(x+y) -1
8y + 4 = 7x + 7y - 1
8y - 7y = 7x - 1 - 4
y = 7x - 5

Therefore:
x = (8y -1) / 3
x = [8(7x - 5) -1] / 3
3x = 56x - 40 -1
56x - 3x = 41
53x = 41
x = 0.774

y = 7(0.774) - 5
y = 0.415

多項式?
你想問咩?

其實你係未打錯問題呢？。。。