Hey guys and garls. I've recently purchased Serge Langs 'Basic Mathematics' and I'm embarrassed to say im not finding it all that basic! Could someone give me a solid discription on how to find Associativity and Commutativity in basic problems so i can progress! If I put a basic problem up could someone step by step take me through how they're solving the problem? I'm more than gutted to get stuck on the first freaking set of problems! Heres one of the exercises : (a - b) + (c - d) = -(b + d) + (a + c) Associativity = ? Commutativity = ? Hope somebody can link me to a good resource or talk me through this problem!