tentukan persamaan garis yang melalui titik (1,4) dan (2,-1)

[tex] \frac{y-y1}{y2-y1} = \frac{x-x1}{x2-x1} [/tex]
[tex] \frac{y-4}{-1-4} = \frac{x-1}{2-1} [/tex]
(kali silang)
y-4 = -5x+5
5x+y=5+4
5x+y=9

y-y1 per y2-y1 = x-x1 per x2-x1
y-4 per -1-4 = x-1 per 2-1
y-4 per -5 = x-1 per 1

y-4 = -5x-5
y = -5x -1