  In this paper, we sharpen and simplify our earlier results based on Thue's
Fundamentaltheorem and use it to obtain effective irrationality measures for
certain roots of polynomials of the form $(x-\sqrt{t})^{n}+(x+\sqrt{t})^{n}$,
where $n \geq 4$ is a positive integer and $t$ is a negative integer. For $n=4$
and $n=5$, we find infinitely many such algebraic numbers.
