(2)点E是线段AD的中点,求直线BE与平面ACD所成角的正弦值. 20.已知函数f(x)?x?3?4lnx. x(1)求f(x)的单调递增区间;
2(2)当0?x?3时,求证:x?2x?3?4xlnx.
21.已知抛物线C:(p?0),焦点为F,直线l交抛物线C于A(x1,y1),y2?2pxB(x2,y2)两点,D(x0,y0)为AB的中点,且|AF|?|BF|?1?2x0.
(1)求抛物线C的方程; (2)若x1x2?y1y2??1,求22. 已知数列?an?中,a1?(1)求证:
x0的最小值. |AB|1?anan?11,an?1?(n?N*). 221?an?1; 2?1??是等差数列;
?an?1?94n,记数列?bn?的前n项和为Sn,求证:Sn? .
15(1?a1)(1?a2)…(1?an)(2)求证:?(3)设bn?
相关推荐: