Answer:
C. (1, -1/2)
Explanation:
The midpoint of a line segment has coordinates that are the average of the end point coordinates.
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M = (A +B)/2 . . . . . . midpoint of segment between A(1, 4) and B(1, -5)
M = ((1, 4) +(1, -5))/2 = (1 +1, 4 -5)/2 = (2, -1)/2
M = (1, -1/2)
The midpoint of the vertical line segment is (1, -1/2).
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Additional comment
The midpoint will always be on the line segment. Since this line segment is vertical with x = 1, the x-coordinate of the midpoint must be 1.