6.已知抛物线y=x2+bx+c的对称轴为x=2,若关于x的一元二次方程-x2-bx-c=0在-1<x<3的范围内有两个相等的实数根,则c的取值范围是( )
| A. | c=4 | B. | -5<c≤4 | C. | -5<c<3或c=4 | D. | -5<c≤3或c=4 |
5.已知x是无理数,且(x+1)(x+3)是有理数,则(1)x2是有理数;(2)(x-1)(x-3)是无理数;(3)(x+1)2是有理数;(4)(x-1)2是无理数4个结论中,正确的有( )
0 294739 294747 294753 294757 294763 294765 294769 294775 294777 294783 294789 294793 294795 294799 294805 294807 294813 294817 294819 294823 294825 294829 294831 294833 294834 294835 294837 294838 294839 294841 294843 294847 294849 294853 294855 294859 294865 294867 294873 294877 294879 294883 294889 294895 294897 294903 294907 294909 294915 294919 294925 294933 366461
| A. | 3个 | B. | 2个 | C. | 1个 | D. | 0个 |