12.已知∠AOB=32°,射线OC⊥OA,则∠COB的度数为( )
| A. | 122° | B. | 58° | ||
| C. | 122°或58° | D. | 以上答案均不正确 |
10.在数0,$\frac{π}{2}$,$-\frac{2}{3}$,0.$\stackrel{•}{0}$$\stackrel{•}{5}$,-1.121121112…,-|-8|中无理数有( )个.
| A. | 1 | B. | 2 | C. | 3 | D. | 4 |
9.下列计算正确的是( )
0 282768 282776 282782 282786 282792 282794 282798 282804 282806 282812 282818 282822 282824 282828 282834 282836 282842 282846 282848 282852 282854 282858 282860 282862 282863 282864 282866 282867 282868 282870 282872 282876 282878 282882 282884 282888 282894 282896 282902 282906 282908 282912 282918 282924 282926 282932 282936 282938 282944 282948 282954 282962 366461
| A. | -8-3=-5 | B. | $(-\frac{1}{3})×3÷3×(-\frac{1}{3})=1$ | C. | 7a+a=7a2 | D. | 4xy2-2xy2=2xy2 |