We prove that if |a1| is large and |a0| is small enough, then
every approximate zero of power series equation P∞
n=0
anxn = 0 can be
approximated by a true zero within a good error bound. Further, we
obtain Hyers-Ulam stability of zeros of the polynomial equation of degree
n, anzn + an−1zn−1 + · · · + a1z + a0 = 0 for a given integer n > 1.