12.用1块A型钢板可制成2块C型钢板、1块D型钢板;用1块B型钢板可制成1块C型钢板、2块D型钢板.现需18块C型钢板,21块D型钢板,可恰好用A型钢板,B型钢板各多少块?设用A型钢板x块,B型钢板y块,可列方程组为( )
| A. | $\left\{\begin{array}{l}2x+y=18\\ x+2y=21\end{array}\right.$ | B. | $\left\{\begin{array}{l}x+y=18\\ 2x-y=21\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}2x+y=21\\ x+2y=18\end{array}\right.$ | D. | $\left\{\begin{array}{l}x+y=21\\ 2x+y=39\end{array}\right.$ |
11.下列各组线段不能构成三角形的是( )
| A. | 3cm,8cm,7cm | B. | 4cm,5cm,6cm | C. | 6cm,8cm,15cm | D. | 8cm,9cm,15cm |
10.下列方程组中,是二元一次方程组的是( )
| A. | $\left\{\begin{array}{l}{xy=1}\\{x+2y=3}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{x=2}\\{3y-x=1}\end{array}\right.$ | C. | $\left\{\begin{array}{l}{\frac{1}{x}+\frac{1}{y}=1}\\{x+y=1}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{x+z=2}\\{x+y=3}\end{array}\right.$ |
8.已知$\left\{\begin{array}{l}{x=2}\\{y=1}\end{array}\right.$是二元一次方程组$\left\{\begin{array}{l}{mx+ny=8}\\{nx-my=1}\end{array}\right.$的解,则2m-n的算术平方根是( )
| A. | 4 | B. | 2 | C. | $\sqrt{2}$ | D. | ±2 |
7.嗨,喜欢上网吗?现在互联网已经成为生活中不可缺少的一部分,假如您在“百度”搜索引擎中输入“乐陵”,能搜索到与之相关的网页约23300000个,将这个数用科学记数法表示为( )
| A. | 2.33×105 | B. | 2.33×106 | C. | 2.33×107 | D. | 2.33×108 |
6.下列长度的线段能组成三角形的是( )
| A. | 3,4,7 | B. | 3,3,6 | C. | 2,5,8 | D. | 6,7,8 |
5.方程x+2y=7在正整数范围内的解有( )
| A. | 1个 | B. | 3个 | C. | 4个 | D. | 无数个 |
4.若关于x的方程4x2-(2k2+k-6)x+4k-1=0的两根互为相反数,则k的值为( )
0 284937 284945 284951 284955 284961 284963 284967 284973 284975 284981 284987 284991 284993 284997 285003 285005 285011 285015 285017 285021 285023 285027 285029 285031 285032 285033 285035 285036 285037 285039 285041 285045 285047 285051 285053 285057 285063 285065 285071 285075 285077 285081 285087 285093 285095 285101 285105 285107 285113 285117 285123 285131 366461
| A. | $\frac{3}{2}$ | B. | -2 | C. | -2或$\frac{3}{2}$ | D. | 2或$\frac{3}{2}$ |