x4 + 2005x2 + 2004x + 2005
=x4-x+2005x2+2005x+2005
=x(x3-1)+2005.(x2+x+1)
=x(x-1)(x2+x+1)+2005.(x2+x+1)
=(x2+x+1)[x(x-1)+2005]
=(x2+x+1)(x2-x+2005)
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