初中數學問題~~~~~~~~~

so x = 4a and y = 9a

13a = 39
a=3

x=4x3=12
y=9x3=27

hope i can help u *~~

2007-03-01 13:29:25 補充：
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x : y = 4 : 9
則4y=9x(比例內外項對應相乘)
y=4/9x
把y=/49x代入x + y = 39 ,得出
4/13x=39
13x=156
x=12
把x=12代入y=4/9x,得出
y=27
驗算
∵4y=9x,則4×27=9×12,等式確實成立.
　x+y=39,則27+12=39,等式確實成立.
∴x=12,y=27是原方程組的解集.

設x=4k , y=9k
so 4k+9k=39
13k=39
k=3

代k=3入公式：
so x=4(3)=12
y=9(3)=27

x = 4a and y = 9a

13a = 39
a=3

x=4x3=12
y=9x3=27

x+y=39--------------(1)
x/y=4/9--------------(2)

Form(1),
x=39-y---------------(3)
Sub(3) into (2)

39-y/y=4/9
4y=351-9y
13y=351
y=27

Sub=27 into(1)
x+27=39
x=12