P(x) = + x^3 - 5x^2 - 25x + 125 There are 2 changes of real sign so by Descartes Rule of signs there are either 2 positive real roots or 0 positive roots.
P(-x) = - x^3 - 5x^2 + 25x + 125 There is just one change of sign so there is exactly 1 real negative root.
125 is a multiple of 5 so By rational root theorem 5 could be a positive root.
P(5) = 125 - 125 - 125 + 125 = 0 so one zero is 5 if we divide the polynomial by (x - 5) we get the quadratic x^2 - 25 (x + 5)(x - 5) = 0
x = 5,-5
so the roots are 5 (multiplicity 2) and -5. 2 real positive zeroes and one real negative zero
