In the shown planar frame made of thin uniform rods, the length of section

$AB$ and

$EF$ is

$l_{1}$ and its thermal linear coefficient of expansion is

$α_{1}.$ The length of section

$CD$ is

$l_{2}$ and its thermal linear coefficient of expansion is

$α_{2}.CBandDE$ are of same length having thermal linear coefficient of expansion

$α_{2}.$ point

$A,B,EandF$ reside on same line, that is, sections

$ABandEF$ overlap. then the ratio of

$l_{2}l_{1} $ for which the distance between end

$A$ and end

$F$ remains the same at all temperatures, is