Find all values of z such that z^4 - 4z^2 +4 = 0.
Let z^2 = a, so we are solving:
a^2 - 4a + 4 = 0
(a - 2)^2 = 0
a = 2
z^2 = 2
\(\boxed{z = \pm \sqrt{2}}\)
+1223 
