2x²-x+2
=2(x²-x/2)+2
=2(x-1/4)²+2-1/8
=2(x-1/4)²+15/8
当x=1/4时,有最小值为15/8
代数式2x²-x+2,当x(=1/4)时,代数式有最(小)值是(15/8)