1. What is an Argand diagram?

An Argand diagram is a way to represent complex numbers using a number plane. The real part of the number is shown on the horizontal axis and the imaginary part on the vertical axis.

2. Can the subtraction of complex numbers be shown on an Argand diagram?

Yes, it is best done by changing the problem to the "addition of the negative complex number"

e.g. a − b = a + (-b)