With these definitions of addition and multiplication, we have { 1 }. The set of complex numbers of the form { 2 } act just like the real numbers R. Further, setting { 3 } gives z = (x, y) = x + iy, and we have { 4 }, that is, i² = -1. Addition and multiplication can now be rewritten as the more usual:

(x₁, y₁) + (x₂, y₂) = (x₁ + x₂, y₁ + y₂),

Match the above missing itens 1, 2, 3, 4 with the selections

(a) i = (0, 1), (b) (x, y)=(x, 0) + (0, 1)(y, 0),
(c) i² = (0, 1).(0, 1) = (-1, 0), (d) (x, 0).