F.3,,wt is the coordinates of S and T?

Explanation as follows:

圖片參考：http://i238.photobucket.com/albums/ff245/chocolate328154/Maths318.jpg?t=1216549380


2008-07-20 18:49:49 補充：
Oh, there is another way to solve the Q which is less complicated.
For details, please refer to taiko_amateur's opinion.
Thx for your suggestion!

Let(a,b) be the coordinate of S

Slope PS = Slope QR
5-b/2-a=4-1/5-4
=3
5-b=3(2-a)
=6-3a
-b=1-3a
b=-1+3a.......(1)

Slope PQ =Slope SR
5-4/2-5=b-1/a-4
1/-3=b-1/a-4
a-4=-3b+3
a=-3b+7..........(2)
Sub(1)into(2)
a=-3(-1+3a)+7
=3-9a+7
10a=10
a=1
Sub a=1 into(1)
b=-1+3(1)
=2
so the coordinate of S is (1,2)


Let(x,y) be the coordinate of T

x=2+4/2
=3

y=5+1/2
=3

so the coordinate of T is (3,3)