Question

Why the order of the coordinates does not matter when calculating length

Answer 1

The formula for calculating length is:
$\sqrt{ (x_b-x_a)^{2} + (y_b-y_a)^{2} }$

We can also write $x_a - x_b$ or $y_a - y_b$
Why it does not matter?
Let's assume we have 2 numbers, a and b.
When we perform a subtraction:
$a-b$, we get another number $c$
When we perform another subtraction:
$b-a$, we get a number $-c$

When we raise $c$ or $-c$ to the power of 2, the result is the same, $c^{2}$.