Whether or not

whether

conjunction

/ˈwɛðər/

 

1 used to express a doubt or choice between two possibilities 

He seemed undecided whether to go or stay.

 It remains to be seen whether or not this idea can be put into practice. 

I asked him whether he had done it all himself or whether someone had helped him. 

I'll see whether she's at home (= or not at home). 

It's doubtful whether there'll be any seats left. 

2 used to show that something is true in either of two cases 

You are entitled to a free gift whether you accept our offer of insurance or not

 I'm going whether you like it or not. 
Whether or not we're successful, 

we can be sure that we did our best.Grammar: if whetherBoth if and whether are used in reporting questions which expect “yes” or “no” as the answer: She asked if/whether I wanted a drink., although whether sounds more natural with particular verbs such as discuss, consider, and decide. When a choice is offered between alternatives, if or whether can be used: We didn’t know if/whether we should write or phone. In this last type of sentence, whether is usually considered more formal and more suitable for written English.

more info :  http://oaadonline.oxfordlearnersdictionaries.com/dictionary/whether