Answer: 
Step-by-step explanation:
By the Pythagorean theorem, the unknown side has length

Therefore,

X-y is positive when y is further away from 0, compared to x. In other words, when y is a larger negative
For example
x = -2
y = -5
x-y = -2-(-5) = -2+5 = 3
The answer is 0.00125139043