Hint:
consider
what does this tell you? What happens if are both odd, both even, one is odd one is even?
i knew that part, i knew that if a,b are even, then a^2 and b^2 would be even, then sum of them would be even, and if a,b were odd, then a^2 would be odd, and b^2 would be odd, but when u add 2 odd numbers, u would get something even
but i don't know about a case when u have a as odd and b as even, i mean i can't proove it by using math
p.s thanks for helping me soo many times