已知抛物线x
2=4y的焦点为F,A、B是抛物线上的两动点,且
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131101230927971042688/SYS201311012309279710426016_ST/0.png)
.过A、B两点分别作抛物线的切线,设其交点为M.
(I)证明
![manfen5.com 满分网](http://img.manfen5.com/res/GZSX/web/STSource/20131101230927971042688/SYS201311012309279710426016_ST/1.png)
为定值;
(II)设△ABM的面积为S,写出S=f(λ)的表达式,并求S的最小值.
考点分析:
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