The length of a metal wire is l1 when the tension is T1 and l2 when the tension is T2. The unstretched length of the wire is
1
\(\frac{T_2l_1 - T_1l_2}{T_2 - T_1}\)
2
\(\frac{T_2l_1 + T_1l_2}{T_2 - T_1}\)
3
\(\frac{T_2l_1 - T_1l_2}{T_2 + T_1}\)
4
\(\frac{T_2l_1 + T_1l_2}{T_2 + T_1}\)