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Coordinates for the midpoint} of a line segment with endpoints A = (x_1,y_1) and B = (x_2,y_2). S = ( (x_1 + x_2) / 2, (y_1 + y_2) / 2 ). Example. Coordinates for the midpoint of a line segment with endpoints A = (-2,3) and B = (4,-9). S = ( (-2+4)/2, (3+(-9))/2 ) = ( 2/2, -6/2) = (1,-3).