I'm unsure about these three, here are my attempts. Please also explain the difference between a predicate and true/false. I assumed it is a predicate when it can be either true or false.

a) Predicate. Negation is ¬(∃n ∈ N n²>n)

b) True. Negation is, "When x<0 there is y such that y^2=x

c) No clue :P

Your help is truly appreciated!