If the line segment bisector divided the original line segment into two equal pieces, and each piece is 2.9 centimeters long, then the total length of the original line segment can be calculated as follows:
\[ \text{Total Length} = 2 \times \text{Length of each piece} = 2 \times 2.9 , \text{cm} = 5.8 , \text{cm} \]
Therefore, the length of Andy’s original line segment is 5.8 cm.