If the line segment bisector divided the original line segment into two equal parts, and each part is 2.9 centimeters long, then we can calculate the total length of the original line segment by simply adding the lengths of the two parts together.
Length of original line segment = Length of one part + Length of one part
Length of original line segment = 2.9 cm + 2.9 cm
Length of original line segment = 5.8 cm
Therefore, Andy's original line segment was 5.8 centimeters long.