18.设a=$\frac{1}{{\sqrt{2}}}$(cos34°-sin34°),b=cos50°cos128°+cos40°cos38°,c=$\frac{1}{2}$(cos80°-2cos250°+1),则a,b,c的大小关系是( )
| A. | a>b>c | B. | b>a>c | C. | c>a>b | D. | a>c>b |
17.已知函数f(x)=x2+bx的图象在点A(1,f(1))处的切线l与直线3x-y+2=0平行,若数列{$\frac{1}{f(n)}}$}的前n项和为Tn,则T2016=( )
| A. | $\frac{2014}{2015}$ | B. | $\frac{2015}{2016}$ | C. | $\frac{2016}{2017}$ | D. | $\frac{2017}{2018}$ |
12.直线mx+y-3m+3=0与抛物线y2=4x的斜率为1的平行弦的中点轨迹有公共点,则m的取值范围是( )
0 229350 229358 229364 229368 229374 229376 229380 229386 229388 229394 229400 229404 229406 229410 229416 229418 229424 229428 229430 229434 229436 229440 229442 229444 229445 229446 229448 229449 229450 229452 229454 229458 229460 229464 229466 229470 229476 229478 229484 229488 229490 229494 229500 229506 229508 229514 229518 229520 229526 229530 229536 229544 266669
| A. | (-$\frac{5}{2}$,0) | B. | (-∞,-$\frac{5}{2}$)∪(0,+∞) | C. | (-∞,0)∪($\frac{5}{2}$,+∞) | D. | (0,$\frac{5}{2}$) |