Question

Consider an even polynomial p(s) given by p(s) = s⁴ + 5s² + 4 + K where K is an unknown real parameter. The complete range of K for which p(s) has all its roots on the imaginary axis is

a) -3 < K < 9/2
b) -5 ≤ K ≤ 0
c) -4 < K < 9/4
d) -6 < K < 5/4