определять - to determine, so определяться is to be determined
употреблять is to use or to consume (regarding food), so употребляться is to be used or to be consumed
облагать is a derivative of a verb класть (which is a correct imperfective of положить), which means to put, so when you say прибыль облагается налогом that really means that someone puts taxes on profits or taxes are put on profits