  We determine the roots in F_{q^3} of the polynomial X^{2q^k+1} + X + c for
each positive integer k and each c in F_q, where q is a power of 2. We
introduce a new approach for this type of question, and we obtain results which
are more explicit than the previous results in this area. Our results resolve
an open problem and a conjecture of Zheng, Kan, Zhang, Peng, and Li.
