If the line segment bisector divides the original line segment into two equal pieces that are each 2.9 centimeters long, then the full length of the original line segment is:
\( 2.9 , \text{cm} + 2.9 , \text{cm} = 5.8 , \text{cm} \).
Therefore, the length of Andy’s original line segment is 5.8 cm.