Rational function
(x-1)(x+1)
(x-2)(x+2)

It is a polynomial of degree 4 with zeros at 1, -1, 2, and -2
If multiplied out , the polynomial would be
(x^2 -1)(x^2 - 4)
x^4 - 5x^2 + 4

The slope of the function is 0.5.