Answer:
DF
Step-by-step explanation:
the mid segment is a line that connects the midpoints. 
 
        
                    
             
        
        
        
The circumcenter is where the perpendicular bisectors meet.
if you sketch the triangle, you will see that it is a right triangle, with the right angle vertex at (2,1)
one perpendicular bisector is x=1, another perpendicular bisector is y=3
they meet at (1,3)
so (1,3) is the answer. 
        
             
        
        
        
Answer:
It is nonlinear if x repeats in any of the sets
Step-by-step explanation:
 
        
             
        
        
        
Answer:
x=11 (read below)
Step-by-step explanation:
7 + x = 18
<em>Subtract 7 from both sides</em>
x=11
It's quite simple because if you do something to one side of the equation, you need to do it to the other because otherwise the equation won't be equal. This is how you need to simplify most problems, by taking something from one side and taking from the other as well.