Persamaan suatu garis lurus melalui titik A (2,-5) dan B (3,4) adalah

y-y1 / y2-y1 = x-x1 / x2-x1
y-(-5) / 4-(-5) = x-2 / 3-2
y+5 / 4+5 = x-2 / 1
y+5 / 9 = x-2 / 1
9(x-2) = 1(y+5)
9x-18 = y+5
9x-y-18-5 = 0
9x-y-23 = 0
atau
9x-y = 23