f(x) = 5x^4 - 10x^3 + x^2 - 2.5x + 20
because it is to the 4th power there are up to 4 roots.
by Descarte's there are 4 changes from positive to negative. So there up to 4 real roots and 2 maybe real and 2 complex.
So, there may be 0 to 4 real roots.
2 maybe complex.
f(-x) = 5(-x)^4 - 10(-x)^3 + (-x)^2 - 2.5(-x) + 20
f(-x) = 5x^4 + 10x^3 + x^2 + 2.5x + 20
there are no negative roots