Sets Question

For number 4 (b) does it read the sum of two squares of odd numbers are not natural numbers? If so can i just show that two odd numbers squared ..... i dont know what to say there cuz natural numbers are wide. Any hints thx

Well S is the set of numbers formed by adding the squares of 2 natural numbers and T is the set of numbers of the form 2m+1 where m is a natural number.

So the question is just asking you to show that if you take the union of these 2 sets, you don't get the whole of the natural numbers. Therefore you just need to look for a counterexample to the claim that S u T is the whole of N i.e. find a natural number that isn't in that union.