Question 187842
solve y^4-4y^2+4=0(hint: set x=y^2 solve for x, then solve for y after finding x) 
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Sub x for y^2
x^2 - 4x + 4 = 0
(x-2)*(x-2) = 0
x = 2
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y^2 = 2
y = +sqrt(2)
y = -sqrt(2)