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 `alpha_(1)`. The length of section `CD` is `l_(2)` and its thermal linear coefficient of expansion is `alpha_(2)`.`CB and DE` are of same length having thermal linear coefficient of expansion `alpha_(2)`. point `A, B, E and F` reside on same line, that is, sections `AB and EF` overlap. then the ratio of `(l_(1))/(l_(2)` for which the distance between end `A` and end `F` remains the same at all temperatures, is