" আমার বই আছে" / I have a book"
" আমার বই নেই"/ I don't have a book"
Students, listen to this song.
This is a sad song, no doubt. But it helps to remember that ' নেই' is the opposite of 'আছে'. It will make you very depressed but you will not make this common mistake again.
" আমার বই আছে নেই"
Skip a couple of lines and then you will come to the right sentence.