Question

Why can an even number be shown as the sum of two aqual addends

Answer 1

Because it's the numbers that brings it together so it makes it makes it an even number but sometimes numbers put together also makes it even though but that's a different thing that you're talking about but I don't know I guess.

Answer 2

Because every even number is a multiple of 2.  So it can always be
split up into two parts that are EQUAL.  And there you have it ... the
original number is the sum of two EQUAL numbers.