lim(x→-∞) (√(4x²-8x+5) +2x+1)
=lim(x→-∞) (√(4x²-8x+5) +2x+1) * (√(4x²-8x+5) -2x-1) / (√(4x²-8x+5) -2x-1)
=lim(x→-∞)[4x²-8x+5 - (2x+1)²] / (√(4x²-8x+5) -2x-1)
=lim(x→-∞)(-12x +4) / (√(4x²-8x+5) -2x-1)
=lim(x→-∞)(12 -4/x) / (√(4-8/x+5/x²) +2+1/x)
此时1/x和1/x²都趋于0
所以
原极限= 12 / (2+2) = 3