daijobu to daijobanai
I've been listening to a lot of Japanese music recently, and have gotten used to how they say their words. But I've also been wondering...why is daijobu changed to daijo*ba*nai? I know the meanings of the words but I've been questioning to myself "why is bu changed to ba, is there a purpose of this?" I'm still learning and would be grateful if anyone could explain :) thank you

Question

Answer

I've never heard it before, however, after some research, it appears to be the same as 大丈夫じゃない　(daijyoubujyanai) but is a very informal version of the word, made by conjugating it like one would a godan verb into the informal negative form.

Source: https://answers.yahoo.com/question/index?qid=20130330223151AAnhfWX

Answer

Let's take a look at the Godan verb (v5b) 遊ぶ (play). For u- verbs, to conjugate to negative form, the last character with the u is changed to its a equivalent and add ない. In this case 遊ぶ becomes 遊ばない. Maybe they're similar, but I have never heard that one before. To be safe, just use だいじょうぶじゃない.

Answer

Two ansers you got are very correct and "daijobanai" is incorrect in Japanese grammar. However, some people use it, especially, in conversation between young people, between close people, so you might hear this word when you watch anime or Japanese drama but I would never like to recommendo you to use it. I hope you understand about it.