18.甲、乙两个人关于年龄有如下对话,甲说:“我是你现在这个年龄时,你是10岁”.乙说:“我是你现在这个年龄时,你是25岁”.设现在甲x岁,乙y岁,下列方程组正确的是( )
| A. | $\left\{\begin{array}{l}{y+10=x-y}\\{x-y=25-x}\end{array}\right.$ | B. | $\left\{\begin{array}{l}{y-10=x-y}\\{x-y=25-y}\end{array}\right.$ | ||
| C. | $\left\{\begin{array}{l}{y-10=x-y}\\{x-y=25+x}\end{array}\right.$ | D. | $\left\{\begin{array}{l}{y-10=x-y}\\{x-y=25-x}\end{array}\right.$ |
17.下列从左到右的变形属于因式分解的是( )
| A. | x2-x-1=x(x-1)-1 | B. | a2-ab=a(a-b) | C. | x2-1=x(x-$\frac{1}{x}$) | D. | (x+2)(x-2)=x2-4 |
16.在数轴上表示不等式-x+1≥0的解集,正确的是( )
0 294831 294839 294845 294849 294855 294857 294861 294867 294869 294875 294881 294885 294887 294891 294897 294899 294905 294909 294911 294915 294917 294921 294923 294925 294926 294927 294929 294930 294931 294933 294935 294939 294941 294945 294947 294951 294957 294959 294965 294969 294971 294975 294981 294987 294989 294995 294999 295001 295007 295011 295017 295025 366461
| A. | B. | C. | D. |