I'm reading the chapter 8 of the Cg tutorial and I could not understand 8.4.1 :
Because all these coordinates lie in the plane of the same triangle, it is possible to derive plane equations for x, y, and z in terms of s and t:
A_0 x + B_0 s + C_0 t + D_0 = 0
A_1 y + B_1 s + C_1 t + D_1 = 0
A_2 z + B_2 s + C_2 t + D_2 = 0
How are these equations derived?