Try this solution:
1) given (3;9) and (-8;1).
The midpoint: ([3-8]/2;[9+1]/2) = (-2.5;5).
2) given (9;9) and (2;1).
The midpoint: ([9+2]/2;[9+1]/2) = (5.5;5).
3) given (-9;9) and (-6;10).
The midpoint: ([-9-6]/2;[9+10]/2)= (-7.5;9.5).
4) given: (-9;-1) and (-4;-1).
The midpoint: ([-9-4]/2;[-1-1]/2)= (-6.5;-1).
5) given (-4;-5) and (5;-3).
The midpoint: ([-4+5]/2;[-5-3]/2) = (0.5;-4).
6) given (-3;5) and (4;5).
The midpoint: ([-3+4]/2;[5+5]/2)= (0.5;5).
7) given (-1;1) and (4;4).
The midpoint: ([-1+4]/2;[1+4]/2)= (1.5;2.5).
8) given (-4;-2) and (5;-3).
The midpoint ([-4+5]/2;[-2-3]/2)= (0.5;-2.5).
The formula of a midpoint:
[tex](\frac{x_a+x_b}{2} ; \frac{y_a+y_b}{2} ).[/tex]
