唔識計@___________@

sing1993

x>0
x(y+z)=5
y(x+z)=10
z(x+y)=13
X=??????????

Royal

下?= =淨係比左個"x>0"比你咋?!
根本就計唔到= =

Kimo

xy+xz=5
xy+yz=10
xz+yz=13

yz-xz=5
xz+yz=13

   yz=5+xz
xz+yz=13

xz+5+xz=13
2xz=8
xz=4

xy+4=5
xy+yz=10
4+yz=13

   xy=1
xy+yz=10
   yz=9

(xyz)^2=36
      xyz=6

xz=4
xy=1
yz=9
xyz=6

xyz/yz=6/9
       x=2/3

xyz/xz=6/4
       y=3/2

xyz/xy=6/1
       z=6

唔知o岩唔o岩 Orz

[ Last edited by Kimo on 2005-10-30 at 11:32 AM ]

綿羊

我竟然唔識計

鴨

Originally posted by Kimo at 2005-10-30 11:22 AM:
.....
(xyz)^2=36
      xyz=6

...

呢道完全唔明.....

Kimo

Originally posted by RX78-2 at 30-10-2005 15:10:

呢道完全唔明.....

xz=4
xy=1
yz=9

xxyyzz=4(9)
so (xyz)^2=36
  √(xyz)^2=√36

路人2號

Originally posted by sing1993 at 2005-10-30 11:01 AM:
x>0
x(y+z)=5
y(x+z)=10
z(x+y)=13
X=??????????

你們教的真快.....
我們現在才做到9b.....T.Tlll

Kimo

Originally posted by 路人2號 at 30-10-2005 17:03:

你們教的真快.....
我們現在才做到9b.....T.Tlll

我也只是F.1而已...樓主跟我同年的
不過唔知點解我maths特別勁，P.2開始年年maths全級第一(晒

Echo21

Originally posted by Kimo at 2005-10-30 11:22:
...

你這樣做小心被扣Presentation分......
少做這類只有一個煩字的數......

x>0
x(y+z)=5
y(x+z)=10
z(x+y)=13


xy + xz = 5 ----------(1)
xy + yz = 10 ----------(2)
xz + yz = 13 ----------(3)

From (3),
yz = 13 - xz ----------(4)

Sub. (4) into (2)
xy - xz = -3
xy = -3 + xz ----------(5)

From (1),
xy = 5 - xz ----------(6)

Sub. (6) into (5)
5 - xz = -3 + xz
2xz = 8
xz = 4 ----------(7)

From (1), (4), (5), we have
xy = -3 + 4 = 1
yz = 13 - 4 = 9 ----------(8)

xy．xz．yz = 1．4．9
(xyz)^2 = 36
xyz = 6 ----------(9)

(9) / (8):
x = 2 / 3//

幻藍

只是比較複雜的代入問題吧......