19.在等腰△AOB中,|AO|=|AB|,点O(0,0),A(1,3),而点B在x轴的正半轴上,则直线AB的方程为( )
| A. | y-1=3(x-3) | B. | y-1=-3(x-3) | C. | y-3=3(x-1) | D. | y-3=-3(x-1) |
13.关于x的方程ax2+2x+a=0至少有一个正的实根,则a的取值范围是( )
| A. | 0<a≤1 | B. | a>0或-1<a<0 | C. | -1≤a<0 | D. | -1≤a≤1 |
12.已知幂函数y=f(x)的图象过点(4,2),则f($\frac{1}{4}$)=( )
| A. | $\sqrt{2}$ | B. | $\frac{1}{2}$ | C. | $\frac{1}{4}$ | D. | $\frac{\sqrt{2}}{2}$ |
11.已知全集U={1,2,3,4,5,6},A={1,2,3,4},B={4,5,6},则集合∁U(A∩B)=( )
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| A. | {4} | B. | {1,2,5,6} | C. | {1,2,3,5,6} | D. | ∅ |