（1）
f(x)=3x²-6x-1
=3(x²-2x)-1
=3(x-1)²-1-3
=3(x-1)²-4
当x=1时,有最小值为-4
(2)f(x)=-2x²+x-1
=-2(x²-x/2)-1
=-2(x-1/4)²-1+1/8
=-2(x-1/4)-7/8
当x=1/4时,有最大值-7/8