persamaan suatu garis yang melalui titik (1,2) dan titik (3,4)

(y-y1) / (y2-y1) = (x-x1) / (x2-x1)
(y-2) / (4-2) = (x-1) / (3-1)
(y-2) / 2 = (x-1) / 2
2(x-1) = 2(y-2)
2x - 2 = 2y - 4
2x - 2y - 2 + 4 = 0
2x - 2y + 2 = 0
-------------------- ÷ 2
x - y + 1 = 0

x2-x1/y2-y1= 4-2/3-1 =2/2 =1
m=1

y-y1=m(x-x1)
y-4 =1(x-3)
y-4 = x-3
y =x+4-3
y =x+1
x-y+1=0