12.下列说法正确的是( )
| A. | 两个无理数的和一定是无理数 | |
| B. | 有理数是有限小数,无理数是无限小数 | |
| C. | $\root{3}{-8}$是有理数 | |
| D. | $\frac{\sqrt{3}}{3}$是分数 |
6.△ABC中,AB=AC=13,BC=10,点P是BC边上的动点,过点P作PD⊥AB于点D,PE⊥AC于点E,则PD+PE的长是( )
0 284753 284761 284767 284771 284777 284779 284783 284789 284791 284797 284803 284807 284809 284813 284819 284821 284827 284831 284833 284837 284839 284843 284845 284847 284848 284849 284851 284852 284853 284855 284857 284861 284863 284867 284869 284873 284879 284881 284887 284891 284893 284897 284903 284909 284911 284917 284921 284923 284929 284933 284939 284947 366461
| A. | $\frac{120}{13}$ | B. | $\frac{120}{13}$或$\frac{60}{13}$ | C. | $\frac{60}{13}$ | D. | 10 |