If you're referring to the different sets of real numbers, it's the ones that you could try to do subtraction and not get an answer that still in that set.
For example, natural numbers (aka 1, 2, 3, 4, ...) are not, because 7 - 11 = -4 and -4 is not a natural number.
Also, whole numbers (aka 0, 1, 2, 3, 4, ...) has the same issue.
Basically any set of real numbers that doesn't include negative numbers will have this issue.
Answer:
A. 
Step-by-step explanation:
1. The standard form of the equation of a circle is 
2. To find the center we require the midpoint of the 2 given points
center =![[\frac{1}{2}(-4-6),\frac{1}{2}(11+5)]](https://tex.z-dn.net/?f=%5B%5Cfrac%7B1%7D%7B2%7D%28-4-6%29%2C%5Cfrac%7B1%7D%7B2%7D%2811%2B5%29%5D)
=(-5,8)
3. The radius is the distance from the centre to either of the 2 given points calculate the radius using the distance formula
d= 
let
and 
r=
--> 
--> 
5a^10-2 I’m pretty sure that’s the right answer