7.已知单项式0.5xa-1y3与3xy4+b是同类项,那么a,b的值分别是( )
| A. | 2,1 | B. | 2,-1 | C. | -2,-1 | D. | -2,1 |
19.规定“!”是一种运算符号,
其中1!=1,
2!=1×2,
3!=1×2×3,
4!=1×2×3×4,…
则$\frac{2017!}{2016!}$的值为( )
0 288748 288756 288762 288766 288772 288774 288778 288784 288786 288792 288798 288802 288804 288808 288814 288816 288822 288826 288828 288832 288834 288838 288840 288842 288843 288844 288846 288847 288848 288850 288852 288856 288858 288862 288864 288868 288874 288876 288882 288886 288888 288892 288898 288904 288906 288912 288916 288918 288924 288928 288934 288942 366461
其中1!=1,
2!=1×2,
3!=1×2×3,
4!=1×2×3×4,…
则$\frac{2017!}{2016!}$的值为( )
| A. | 2014 | B. | 2015 | C. | 2016 | D. | 2017 |