the length of a metal wire is (1, when the tension in it is t1 and is (2 when the tension is t2. the natural length of the wire is :
a) l₁ + l₂ / 2
b) √l₁ l₂
c) l₁T₂ - l₂T₁ / T₂-T₁
d) l₁T₂ + l₂T₁ /T₂+ T₁