數學問題~急~

1.你係咪打漏左 d 野..(a+2):b = 3:4:7 (有三個數??)

2a)
x:y=4:9
x/y = 4/9
x = 4y/9

2b)
x+y=39
(4y/9)+y=39
4y+9y = 39*9 (成條式乘 9)
13y = 351
y = 27

2007-06-12 15:16:58 補充：
(a 2): (a 5):b =3:4:7ie. (a 2)/(a 5) = 3/4, (a 2)/b = 3/7 & (a 5)/b = 4/74(a 2) = 3(a 5)4a 8 = 3a 15a = 7(a 2)/b = 3/7(7 2)/b = 3/79*7 = 3bb = 21Therefore, a = 7 & b = 21.

1)
(a+2) :b =3:4:7
左邊兩個比又點會等於右邊三個比
打少左野

2a)
x/y = 4/9
x = 4y/9

b)
4y/9 + y = 39
(4/9 + 1) y = 39
(13/9) y = 39
y = 27
x = 12