Right now were having a functions test soon, and i need quick help fast please

One Q is :

Explain, without graphing, why 2x^2 -1=y^2 is not a function, explain specifically what rule it breaks.

2Q:

Determine algebraically if the funciton is even,odd or neither. Justidy your answer.

f(x)=2x^2 +1

( i know we have to do the f(-x) and -f(-x) stuff, but i dont understand how to do it)

PLEASE HELP