14.求1+2+22+23+…+22016的值,可设S=1+2+22+23+…+22016,于是2S=2+22+23+…+22017,因此2S-S=22017-1,所以S=22017-1.我们把这种求和方法叫错位相减法.仿照上述的思路方法,计算出1+5+52+53+…+52016的值为( )
| A. | 52017-1 | B. | 52016-1 | C. | $\frac{{5}^{2017}-1}{4}$ | D. | $\frac{{5}^{2016}-1}{4}$ |
13.能使等式$\sqrt{\frac{x}{x-3}}$=$\frac{\sqrt{x}}{\sqrt{x-3}}$成立的条件是( )
0 284555 284563 284569 284573 284579 284581 284585 284591 284593 284599 284605 284609 284611 284615 284621 284623 284629 284633 284635 284639 284641 284645 284647 284649 284650 284651 284653 284654 284655 284657 284659 284663 284665 284669 284671 284675 284681 284683 284689 284693 284695 284699 284705 284711 284713 284719 284723 284725 284731 284735 284741 284749 366461
| A. | x>0 | B. | x≥3 | C. | x≥0 | D. | x>3 |