Recall that the function f is the even function if it is symmetric about y-axis; that is, for any x in domain of f, f(-x) = f(x). The function f is odd function if rotating it 180 degrees about origin does not change graph; which is, for any x in domain of f, f(-x) = -f(x). Illustrate that any function f can be written as sum of even function with the odd function.