Answer:
x = 1 or -1
x = -2 or 2
Explanation:
x4 - 5x2 + 4 = 0
x4 - 4 x2 - x2 + 4 =0
x2 ( x2 - 4 ) - 1 ( x2 - 4 ) = 0
( x2 - 1 ) ( x2 - 4 ) =
x2 - 1 = 0 or x2 - 4 = 0
x2 = 1 x2 = 4
x = 1 or -1 x = -2 or 2
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