persamaan garis yg melalui titik (2,1) dan (3,6) adalah

(y-y1)/(y2-y1) = (x-x1)/(x2-x1)
(y-1)/(6-1) = (x-2)/(3-2)
(y-1)/5 = (x-2)/1
y-1 = 5x-10
y = 5x -9