This Argand diagram
shows how complex numbers a and b are added to produce the
complex number c. This addition is similar to the "parallelogram law"
for adding vectors.
Summary
the Argand diagram illustrates
a + b = c, where a, b and c are
complex numbers
if a = c + di and
b = e + fi, then c = a + b = (c+e) +
(d+f)i