+14915 Find all values of z such that z^4 - 4z^2 +4 = 0.
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\(Replace\ z^2\ with\ x.\)
\(x^2-4x+4=0\)
p q
\(x=-\frac{p}{2}\pm \sqrt{(\frac{p}{2})^2-q}\\ x=2\pm \sqrt{2^2-4}\\ x=2\)
\(Replace\ x\ with\ z ^ 2. \)
\(z^2=2\\ z=\pm \sqrt{2}\)
\(z\in \{-\sqrt{2},\sqrt{2}\}\)
\(z\in \{-1.414,1.414\}\)
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