A
D
a		 B
E
b		 C
F
c		 x
y
w		 = Ax + By + Cw
Dx + Ey + Fw
ax + by + cw

If our point comes from the Cartesian coordinates then wh = 1.

x' = A x + B y + C
y' = D x + E y + F
w' = a x + b y + c

To get back to the Cartesian coordinates, let's make our w' = 1.

x' = (A x + B y + C) / (a x + b y + c)
y' = (D x + E y + F) / (a x + b y + c)
w' = 1

←
→