6.已知Sn是数列{an}的前n项和,a1=1,a2=2,a3=3,若数列{an+an+1+an+2}是以2为公比的等比数列,则S26的值为( )
| A. | $\frac{3({2}^{27}-1)}{7}$ | B. | $\frac{3({2}^{27}-2)}{7}$ | C. | $\frac{3({2}^{26}-1)}{7}$ | D. | $\frac{3({2}^{26}-2)}{7}$ |
4.椭圆$\frac{{x}^{2}}{{a}^{2}}$+$\frac{{y}^{2}}{{b}^{2}}$=1(a>b>0)的左、右焦点是F1、F2,M为椭圆上与F1、2不共线的任意一点,I为△MF1F2的内心,延长MI交线段F1F2于点N,则|MI|:|IN|的值等于( )
| A. | $\frac{a}{b}$ | B. | $\frac{a}{c}$ | C. | $\frac{b}{c}$ | D. | $\frac{c}{a}$ |
1.已知集合A={x|y=$\sqrt{-{x}^{2}+x+2}$},B={y|y=2x},则A∩B=( )
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| A. | ∅ | B. | [0,2] | C. | (0,2] | D. | [-1,2] |