4.一个两位数的十位数字与个位数字的和是8,把这个两位数加上18,结果恰好成为数字对调后组成的两位数,求这个两位数,设个位数字为x,十位数字为y,所列方程组正确的是( )
| A. | $\left\{\begin{array}{l}{x+y=8}\\{xy+18=yx}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x+y=8}\\{10(x+y)+18=yx}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{x+y=8}\\{10x+y+18=yx}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x+y=8}\\{x+10y+18=10x+y}\end{array}\right.$ |
17.计算(-3)×4的结果是( )
| A. | 12 | B. | -12 | C. | -1 | D. | -7 |
16.
如图,点A、B、C都在⊙O上,且BO=BC,则∠BAC=( )
0 283850 283858 283864 283868 283874 283876 283880 283886 283888 283894 283900 283904 283906 283910 283916 283918 283924 283928 283930 283934 283936 283940 283942 283944 283945 283946 283948 283949 283950 283952 283954 283958 283960 283964 283966 283970 283976 283978 283984 283988 283990 283994 284000 284006 284008 284014 284018 284020 284026 284030 284036 284044 366461
| A. | 30° | B. | 40° | C. | 50° | D. | 60° |