The length of metallic wire is l1 when tension in it is T1. It is l2 when the tension is T2. The original length of the wire will be:
1
\(\frac{{{l_1} + {l_2}}}{2}\)
2
\(\frac{{{T_2}{l_1} + {T_1}{l_2}}}{{{T_1} + {T_2}}}\)
3
\(\frac{{{T_1}{l_1} - {T_2}{l_2}}}{{{T_2} - {T_1}}}\)
4
\(\frac{{{T_2}{l_1} - {T_1}{l_2}}}{{{T_2} - {T_1}}}\)