lossless decomposition of database table

Question

suppose we have a table(relational schema actually) R(A, B, C, D, E) with functional dependency (C, D)=> E . which one of these below is a lossless/nonless decomposition and what is the problem of the other one? first decomposition: R_1(A, B) and R_2(C, D, E) second decomposition: R_1(A, B, C, D) and R_2(A, C, D, E)
a simple question from a beginner, though! I've searched the internet, but in the tutorials, they only talk about the necessary conditions for correct operation and do not talk about why some decompositions are wrong.