7.如果关于x的方程ax2+x-1=0有实数根,则a的取值范围是( )
| A. | a$≥-\frac{1}{4}$ | B. | a$≥-\frac{1}{4}$且a≠0 | C. | a$>-\frac{1}{4}$ | D. | a$>-\frac{1}{4}$且a≠0 |
6.已知一元二次方程3x2-2x+1=0,则它的二次项系数为( )
| A. | 1 | B. | -2 | C. | 3 | D. | 3x2 |
5.在四边形ABCD中,AB=CD,BC=DA,则下列结论不一定成立的是( )
| A. | AB=CB | B. | ∠B=∠D | C. | AB∥CD | D. | ∠A+∠B=180° |
4.已知四边形ABCD是平行四边形,下列结论中不正确的是( )
| A. | 当AB=AD时,它是菱形 | B. | 当AC=BD时,它是正方形 | ||
| C. | 当∠ABC=90°时,它是矩形 | D. | 当AC⊥BD时,它是菱形 |
3.
0 286576 286584 286590 286594 286600 286602 286606 286612 286614 286620 286626 286630 286632 286636 286642 286644 286650 286654 286656 286660 286662 286666 286668 286670 286671 286672 286674 286675 286676 286678 286680 286684 286686 286690 286692 286696 286702 286704 286710 286714 286716 286720 286726 286732 286734 286740 286744 286746 286752 286756 286762 286770 366461
| 抛物线 | 开口方向 | 顶点坐标 | 对称轴 |
| y=3(x-2)2+4 | 向上 | (2,4) | x=2 |
| y=(x+2)2 | 向上 | (-2,0) | x=-2 |
| y=-$\frac{1}{3}{x}^{2}$+5 | 向下 | (0,5) | x=0 |
| y=y=$\frac{1}{6}(x+3)^{2}+1$ | $\frac{1}{6}(x+3)^{2}+1$向下 | (-3,1) | x=-3 |