Which property of addition is shown below?
If x = 1 + 2i and y = -1 - 2i, then x + y = 0.

Solution:

The additive inverse identity of complex numbers says that there exists a unique complex number -z for z such that z + (-z) = 0.

In the above equation, the identity used is additive inverse.

Where x = 1 + 2i is z and y = -1 - 2i is (-z)

then x + y = 0.

Which property of addition is shown below?
If x = 1 + 2i and y = -1 - 2i, then x + y = 0.

Summary:

The property of addition that satisfies the equation is additive inverse.