13.记$\underset{\stackrel{k}{Ⅱ}}{n=1}$an为数列{an}的前k项积,已知正项等比数列{an}中,若a3,a7是方程x2-6x+2=0的两根,则$\underset{\stackrel{9}{Ⅱ}}{n=1}$an=( )
A. | 8$\sqrt{2}$ | B. | 16$\sqrt{2}$ | C. | 16 | D. | 32 |
11.下列命题是假命题的是( )
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A. | 若$\overrightarrow{a}•\overrightarrow{b}$=0($\overrightarrow{a}$≠0,$\overrightarrow{b}$≠0),则$\overrightarrow{a}⊥\overrightarrow{b}$ | B. | 若|$\overrightarrow{a}$|=|$\overrightarrow{b}$|,则$\overrightarrow{a}$=$\overrightarrow{b}$ | ||
C. | 若ac2>bc2,则a>b | D. | 若α=60°,则cosα=$\frac{1}{2}$ |