Answer :
Cannot is formal, while can't in informal.
"Cannot" and "can not" are interchangeable, but when you are asking question for example:
"why can't I...", you can also say "why can I not..." (which is more formal), but you can't say "why cannot I..."
"Cannot" and "can not" are interchangeable, but when you are asking question for example:
"why can't I...", you can also say "why can I not..." (which is more formal), but you can't say "why cannot I..."
