9.在正方体ABCD-A1B1C1D1中任取一点P,则点P在三棱锥B1-ABC的概率为( )
A. | $\frac{1}{2}$ | B. | $\frac{1}{3}$ | C. | $\frac{1}{6}$ | D. | $\frac{1}{12}$ |
6.已知函数f(x)=$\left\{\begin{array}{l}{(5-a)x+a-6,x≤4}\\{2{a}^{x-3},x>4}\end{array}\right.$,数列{an}满足an=f(n)(n∈N+),且数列{an}是单调递增数列,则实数a的取值范围是( )
A. | (1,5) | B. | (2,5) | C. | ($\frac{14}{5}$,5) | D. | [$\frac{14}{5}$,5) |
5.若函数f(x)=x3-$\frac{3}{2}$ax2+a在R上存在三个零点,则实数a的取值范围是( )
A. | a>$\sqrt{2}$ | B. | a>$\sqrt{2}$或a<-$\sqrt{2}$ | C. | a<-$\sqrt{2}$ | D. | a<-1 |
4.设C是∠AOB所在平面外的一点,若∠AOB=∠BOC=∠AOC=θ,其中θ是锐角,而OC与平面AOB所成角的余弦值等于$\frac{\sqrt{3}}{3}$,则θ的值为( )
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A. | 30° | B. | 45° | C. | 60° | D. | 75° |