A planar lamina is made of thin uniform rods. The length of section AB and EF is L1 and its coefficient is α1. The length of CD is L2 and its coefficient is α2. CB and DE are of same length having coefficient α1α2=3.5 Points A, B, E and F reside on the same line that is sections AB and EF overlap. Then find the ratio of l2l1 for which the distance between end A and end F remain same at all temperatures