persamaan garis lurus melalui titik a (3,-2) dan titik B(-1,2) adalah

(x1,y1) → (3,-2)
(x2,y2) → (-1,2)
Pers. garisnya :
y-y1 / y2-y1 = x-x1 / x2-x1
..y+2 / 2+2 = x-3 / -1-3
.......-4(y+2) = 4(x-3)
............-y-2 = x-3
.............x+y = 1