.......pakai cara nya ya

persamaan garis melalui (x1, y1) dan (x2, y2)
(y - y1)/(y2 -y1) = (x - x1)/(x2 - x1)
A( 2,1) dan B (4,5)
(y - 1)/(5-1) = (x - 2)/(4-2)
(y - 1)/4 = (x - 2)/2
(y -1).2 = 4.(x-2)
2y - 2 = 4x -8
2y = 4x - 8 +2
2y = 4x -6
y = (4x -6)/2
y = 2x - 3