I'll do one; you try the others.
True or false? Negative numbers are closed under addition.
True: for any positive a,b
-a + -b = -(a+b)
True or false? Negative numbers are closed under addition. Give a counterexample
True or false? Prime numbers are closed under subtraction. Give a counterexample
True or false? Natural numbers are closed under division. Give a counterexample
2 answers
False