In this paper, we determine the permutation properties of the polynomial x^3+x^q+2−x^4q−1 over the finite field Fq2 in characteristic three. Moreover, we consider the trinomials of the form x^4q−1 +x^2q+1 ±x^3. In particular, we first show that x^3 +x^q+2 −x^4q−1 permutes F_q^2 with q = 3^m if and only if m is odd. This enables us to show that the sufficient condition in [35, Theorem 4] is also necessary. Next, we prove that x^4q−1 + x^2q+1 − x^3 permutes F_q^2 with q = 3^m if and only if m is congruent to 0 modulo 4. Consequently, we prove that the sufficient condition in [20, Theorem 3.2] is also necessary. Finally, we investigate the trinomial x^4q−1 +x^2q+1 +x^3 and show that it is never a permutation polynomial of F_q^2 in any characteristic. All the polynomials considered in this work are not quasi-multiplicative equivalent to any known class of permutation trinomials.
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