Question 672282
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Hi,
f(x) = x^4 + 22x^2 + 21
f(x) = (x^2 + 21)(x^2+1)
 (x^2 + 21)(x^2+1)= 0 ,  
 (x^2 + 21)= 0,  x = ± {{{i*sqrt(21)}}} 
0r(x^2+1)= 0     x = ± i