8.若二次函数y=x2+mx的对称轴是直线x=3,则m的值为( )
| A. | 3 | B. | -3 | C. | 6 | D. | -6 |
4.
如图,Rt△ABC中,∠C=90°,BD是∠ABC的平分线,DE⊥AB于点E,AB=20cm,BC=12cm,△ABC的面积为96cm2,则DE的长是( )
0 288572 288580 288586 288590 288596 288598 288602 288608 288610 288616 288622 288626 288628 288632 288638 288640 288646 288650 288652 288656 288658 288662 288664 288666 288667 288668 288670 288671 288672 288674 288676 288680 288682 288686 288688 288692 288698 288700 288706 288710 288712 288716 288722 288728 288730 288736 288740 288742 288748 288752 288758 288766 366461
| A. | 4cm | B. | 6cm | C. | 8cm | D. | 10cm |