∵3x²－2x＋4
=3(x²-2/3x+4/3)
=3(x²-2/3x+1/9-1/9+4/3)
=3(x-1/3)²-1/3+4
=3(x-1/3)²+11/3≥11/3
∴3x²－2x＋4的值不小于11／3