14.已知向量$\overrightarrow{a},\overrightarrow{b}$是单位向量,$\overrightarrow{a}•\overrightarrow{b}$=0,若|$\overrightarrow{c}-\overrightarrow{a}-\overrightarrow{b}$|=1,则|$\overrightarrow{c}$|的最大值为( )
| A. | 2 | B. | $\sqrt{2}$ | C. | 3 | D. | $\sqrt{2}+1$ |
10.若Sn=cos$\frac{π}{8}$+cos$\frac{2π}{8}$+…+cos$\frac{nπ}{8}$(n∈N+),则在S1,S2,…,S2015中,正数的个数是( )
| A. | 882 | B. | 756 | C. | 750 | D. | 378 |
9.已知等差数列{an}中,a2+a4=16,a1=1,则a5的值是( )
0 234440 234448 234454 234458 234464 234466 234470 234476 234478 234484 234490 234494 234496 234500 234506 234508 234514 234518 234520 234524 234526 234530 234532 234534 234535 234536 234538 234539 234540 234542 234544 234548 234550 234554 234556 234560 234566 234568 234574 234578 234580 234584 234590 234596 234598 234604 234608 234610 234616 234620 234626 234634 266669
| A. | 15 | B. | 30 | C. | 31 | D. | 64 |