To start off, you can divide the right side of the equation by x to get rid of most of the x's so you get the polynomial x^4 - 10x^2 + 9. This means that f(x) = x^4 - 10x^2 + 9x. By factoring the right side of the equation, you get f(x) = (x^2 - 1)(x^2 - 9). I think the minimum value is 1 and the maximum value is 3.
