15.已知锐角α满足$cos2α=sin(\frac{π}{4}+α)$,则sin2α等于( )
A. | $\frac{1}{2}$ | B. | $-\frac{1}{2}$ | C. | $\frac{{\sqrt{2}}}{2}$ | D. | $-\frac{{\sqrt{2}}}{2}$ |
12.函数y=x2-x+2在[a,+∞)上单调递增是函数y=ax为单调递增函数的( )
A. | 充分不必要条件 | B. | 必要不充分条件 | ||
C. | 充要条件 | D. | 既不充分又不必要条件 |
6.函数f(x)=($\frac{1}{2}$)${\;}^{\sqrt{{x}^{2}-x-2}}$的单调递增区间为( )
0 251734 251742 251748 251752 251758 251760 251764 251770 251772 251778 251784 251788 251790 251794 251800 251802 251808 251812 251814 251818 251820 251824 251826 251828 251829 251830 251832 251833 251834 251836 251838 251842 251844 251848 251850 251854 251860 251862 251868 251872 251874 251878 251884 251890 251892 251898 251902 251904 251910 251914 251920 251928 266669
A. | (-∞,-1] | B. | [2,+∞) | C. | (-∞,$\frac{1}{2}$) | D. | ($\frac{1}{2}$,+∞) |