1.下列命题正确的是( )
| A. | 在△ABC中,角A,B,C的对边分别是a,b,c,则a>b是cos A<cos B的充要条件 | |
| B. | 命题p:对任意的x∈R,x2+x+1>0,则¬p:对任意的x∈R,x2+x+1≤0 | |
| C. | 已知p:$\frac{1}{x+1}$>0,则¬p:$\frac{1}{x+1}$≤0 | |
| D. | 存在实数x∈R,使sin x+cos x=$\frac{π}{2}$成立 |
20.在锐角△ABC中,AB=3,AC=4,SABC=3$\sqrt{3}$,则cosA=( )
| A. | $\frac{1}{2}$ | B. | $\frac{\sqrt{3}}{2}$ | C. | ±$\frac{1}{2}$ | D. | ±$\frac{\sqrt{3}}{2}$ |
19.若α,β为锐角,且满足cosα=$\frac{4}{5}$,cos(α+β)=$\frac{5}{13}$,则sinβ的值为( )
| A. | -$\frac{16}{65}$ | B. | $\frac{33}{65}$ | C. | $\frac{56}{65}$ | D. | $\frac{63}{65}$ |
18.三个数70.3,0.37,㏑0.3,的大小顺序是( )
0 234318 234326 234332 234336 234342 234344 234348 234354 234356 234362 234368 234372 234374 234378 234384 234386 234392 234396 234398 234402 234404 234408 234410 234412 234413 234414 234416 234417 234418 234420 234422 234426 234428 234432 234434 234438 234444 234446 234452 234456 234458 234462 234468 234474 234476 234482 234486 234488 234494 234498 234504 234512 266669
| A. | 70.3,0.37,㏑0.3 | B. | 70.3,㏑0.3,0.37 | C. | 0.37,70.3,㏑0.3 | D. | ㏑0.3,70.3,0.37, |