How I could show a image background with a variable?

I try to explain it :

I have a div called "entrante1_ctn" that must contain a background image. This code works but I don't want to do this...

sym.getComposition().getStage().getSymbol("entrantes_sym").$("entrante1_ctn").css('backgro undImage','url(images/entrantes/entrante1.png)');

I would like to do somtehing like this...

sym.getComposition().getStage().getSymbol("entrantes_sym").$("entrante1_ctn").css('backgro undImage','url( variable )');

This variable is an element of array but this code don't work :

sym.getComposition().getStage().getSymbol("entrantes_sym").$("entrante1_ctn").css('backgro undImage','url( ent_1[0] )');

please, helpp!!!!!!