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b.x4+√x2+2005=2005
<=>x4+x2+14=x2+2005-√x2+2005+14
<=>(x2+12)2-(√x2+2005−12)2=0
<=>(x2+√x2+2005)(x2-√x2+2005+1)=0
<=>x2-√x2+2005+1=0(x2+√x2+2005≠0)
<=>x2+2005-√x2+2005+14=80174
<=>(√x2+2005−12)2=80174
<=>√x2+2005=±√80172+12
<=>√x2+2005=√80172+12 (√x2+2005>0)
<=>x2=−1+√80172
<=>x=±√−1+√80172
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