To find the length of Andy's original line segment, we can use the information given about the line segment bisector.
Since a bisector divides a line segment into two equal parts, if each piece is 2.9 centimeters long, then the total length of the original line segment can be calculated by adding both pieces together:
\[ \text{Total Length} = 2.9 , \text{cm} + 2.9 , \text{cm} \]
Calculating that gives us:
\[ \text{Total Length} = 5.8 , \text{cm} \]
Therefore, Andy's original line segment was 5.8 cm long.