5.用数学归纳法证明$\frac{1}{n+1}+\frac{1}{n+2}+…+\frac{1}{2n}>\frac{13}{24}$,由n=k到n=k+1左边需添加的项为( )
A. | $\frac{1}{2(k+1)}$ | B. | $\frac{1}{2k+1}+\frac{1}{2k+2}-\frac{1}{k+1}$ | ||
C. | $\frac{1}{2k+1}+\frac{1}{2k+2}+\frac{1}{k+1}$ | D. | $\frac{1}{2k+1}+\frac{1}{2k+2}$ |
1.已知函数f(x)=logsinβ(x2+ax+3)在区间(-∞,1)上递增,则实数a的取值范围是( )
0 251752 251760 251766 251770 251776 251778 251782 251788 251790 251796 251802 251806 251808 251812 251818 251820 251826 251830 251832 251836 251838 251842 251844 251846 251847 251848 251850 251851 251852 251854 251856 251860 251862 251866 251868 251872 251878 251880 251886 251890 251892 251896 251902 251908 251910 251916 251920 251922 251928 251932 251938 251946 266669
A. | (-4,-2] | B. | [-4,-2] | C. | (-4,+∞) | D. | (-∞,-2) |