Hi everyone! I want to ask something about differentials. I often visit this forum and I saw people write that dx is something infinitesimal. Well but i read some books about differentials.Some of them define dx equals [delta x] and some of them seem not to consider dx as infinitesimal thing. Is there a contradiction? Which one is true? Can anyone give a original defintion for differentials? Any reply or materials are appreciated! Thank you very much!