=30﹣25
=5(元).
答:每盆便宜5元
(I)求g(x)的极值;
(II)证明:对任意实数x∈R,都有f′(x)≥x﹣2ax+1恒成立:
(Ⅲ)若f(x)≥x+1在x≥0时恒成立,求实数a的取值范围.