Question 13405
A function f(x) is defined as being even if f(x) = f(-x)
and odd if f(-x) = -f(x) since this does not equal f(x)

In the given equation {{{ x^2 + y^2}}} = 16

Even if we put -x and -y in place of x and y the value does not change since the square on both variables removes the negative sign.

Hence the expression is Even