2x²+x+1=2[x²+(1/2)x]+1=2[x²+2×(1/4)x+(1/4)²]-1/8+1=2(x+1/4)²+7/8=2(4x+1)²/16+7/8=[(4x+1)²+7]/8=[(4x+1)²-(i√7)²]/8=(4x+1+i√7)(4x+1-i√7)/8