請問d人點諗到只要任何一個x,y座標符合ax+by+c=0依條equation...

我唔知有冇錯，不過就寫出來先啦。

用兩點做例子：

A ( 1 , 0) and B ( 3 , 5 )

slope of AB :

( 5 - 0 ) / ( 3 - 1 )

= 5 / 2

然後那條線，AB 便會是：

( 5 / 2 ) x + c = y

Sub ( 1 , 0) into the equation , we have :

( 5 / 2 ) (1) + c = 0

5 / 2 + c = 0

c = - ( 5 / 2 )

所以：

( 5 / 2 ) x - ( 5 / 2 ) = y

5x - 5 = 2y

5x - 2y - 5 = 0

得出這條式後，

如果你知道一點在那條線上面，

但你只知它的 x ,

就當佢係 2 先啦，

然後你就會知道它的 y ：

5x - 2y - 5 = 0

5 ( 2 ) - 2y - 5 = 0

10 - 2y - 5 =0

5 - 2y = 0

y = 5 / 2

之後，我地就可以知道：

( 1 , 0 ) , ( 2 , 5 / 2 ) and ( 3 , 5 )

都係在 " 5x - 2y - 5 = 0 " 上面

其實呢，上面的東西都只是我諗出黎的，

我不知古人諗咩。

而且好似好亂咁......

ax+by+c=0 this equation is the equation of a line and all points on the line will satisfy the equation.so if you know the x,y座標 of a spot, u put x and y into the equation, and if it equals 0, then the point is on the line.

the equation can be calculated by this method.

1. find the slope of the line

2. find two points on the spot which their x-y coordinates are known.

3. let the two points be point A(x1, y1) and point B(x2, y2)
slope of line will be (y1-y2)/(x1-x2)

4. find a point(can be point A or B), the the equation is: m(X-x1)=(Y-y1)
(where m=slope, X and Y = the x-y coordinates of the point)