直線的方程2

As follows:

圖片參考：http://h.imagehost.org/0555/ScreenHunter_03_Sep_21_20_40.gif

3(a) The have two ponits which is (-1,5) and (4,3)
By using two point form
the equation of the str line is
y-5 y-3
____ =___
x+1 x-4

(y-5)(x-4) =(x+1)(y-3)
xy-5x-4y+20=xy+y-3x-3

2x+5y-23=0 L= -2
----
5

3b two points (-7,2) (-3,-4)

same method

(y-2)(x+3)=(y+4)(x+7)

6x+4y+34=0
3x+2y+17=0 L= -3
___
2