(2010•保定三模)已知抛物线y=-2x2+2kx-3的顶点在x轴的负半轴上,则k值等于(  ) A.6 B.-6 C.6 D.-6

问题描述:

(2010•保定三模)已知抛物线y=-2x2+2kx-3的顶点在x轴的负半轴上,则k值等于(  )
A.

6

B. -
6

C. 6
D. -6

∵抛物线y=-2x2+2kx-3的顶点在x轴的负半轴上,

4k2−4×(−2)×(−3)
4×(−2)
=0
2k
2×(−2)
<0

解得:k=-
6

故选B.