9.关于直线a,b,c以及平面α,β,给出下列命题:
①若a∥α,b∥α,则a∥b
②若a∥α,b⊥α,则a⊥b
③若a?α,b?α,且c⊥a,c⊥b,则c⊥α
④若a⊥α,a∥β,则α⊥β.
其中错误的命题是( )
①若a∥α,b∥α,则a∥b
②若a∥α,b⊥α,则a⊥b
③若a?α,b?α,且c⊥a,c⊥b,则c⊥α
④若a⊥α,a∥β,则α⊥β.
其中错误的命题是( )
A. | ①② | B. | ②④ | C. | ①③ | D. | ②③ |
8.抛物线y=$\frac{1}{16}$x2的准线方程是( )
A. | y=-2 | B. | x=-2 | C. | x=-4 | D. | y=-4 |
7.$sin(-\frac{43π}{6})$的值为( )
A. | $\frac{1}{2}$ | B. | $-\frac{1}{2}$ | C. | $\frac{{\sqrt{3}}}{2}$ | D. | $-\frac{{\sqrt{3}}}{2}$ |
6.设$\overrightarrow{a}$、$\overrightarrow{b}$、$\overrightarrow{c}$是非零向量,下列命题正确的是( )
A. | ($\overrightarrow{a}$•$\overrightarrow{b}$)•$\overrightarrow{c}$=$\overrightarrow{a}$•($\overrightarrow{b}$•$\overrightarrow{c}$) | B. | |$\overrightarrow{a}$-$\overrightarrow{b}$|2=|$\overrightarrow{a}$|2-2|$\overrightarrow{a}$||$\overrightarrow{b}$|+|$\overrightarrow{b}$|2 | ||
C. | 若|$\overrightarrow{a}$|=|$\overrightarrow{b}$|=|$\overrightarrow{a}$+$\overrightarrow{b}$|,则$\overrightarrow{a}$与$\overrightarrow{b}$的夹角为60° | D. | 若|$\overrightarrow{a}$|=|$\overrightarrow{b}$|=|$\overrightarrow{a}$-$\overrightarrow{b}$|,则$\overrightarrow{a}$与$\overrightarrow{b}$的夹角为60° |
5.向量$\overrightarrow a=(-2,1)$,$\overrightarrow b=(λ,1)$,若$\vec a$与$\vec b$的夹角为钝角,则λ的范围( )
A. | $(\frac{1}{2},2)∪(2,+∞)$ | B. | (2,+∞) | C. | $(-∞,-\frac{1}{2})$ | D. | $(\frac{1}{2},+∞)$ |
4.设各项为正的等比数列{an}的公比q≠1,且a3,a5,a6成等差数列,则$\frac{{a}_{3}+{a}_{5}}{{a}_{4}+{a}_{6}}$的值为( )
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A. | $\frac{{\sqrt{5}+1}}{2}$ | B. | $\frac{{\sqrt{5}-1}}{2}$ | C. | $\frac{1}{2}$ | D. | 2 |