In what situations would someone use one of the following forms over the others when requesting the action やる?
- やってくれる?
- やってくれない?
- やってくれ
- やって(ください)
My assumption is that the first two would translate more along the lines of "Could you do it?" while the last two would translate to "Please do it." (Am I correct?) But between (1) and (2) and between (3) and (4), what are the differences?