To find the length of Andy's original line segment, we know that the line segment bisector divides the segment into two equal parts. If each part is 2.9 centimeters long, we can determine the total length of the original line segment by doubling the length of one of the segments.
The total length \( L \) of the original line segment is calculated as follows:
\[ L = 2 \times 2.9 , \text{cm} \]
Calculating this gives:
\[ L = 5.8 , \text{cm} \]
Thus, the length of Andy's original line segment is 5.8 centimeters.