In the other hand, The first one was told by somebody and the second one was written somewhere in the internet. I really got confused. By the way, somebody told me that it may do with minus. But in our notes, it's only addition. However, look at this Somebody asked me, how many terms are there in this expression, I said Three! But somebody corrected me that there were four. So, meaning separated by either an addition or subtraction not addition only? Thank you very much.