利用公式法求下列二次函数的对称轴和顶点坐标 y=1/3x平方-1/2x-2

y=1/3x²-1/2x-2
a=1/3 ,b=-1/2 ,c=-2,对称轴为x=-b/(2a)；顶点坐标为[ -b/(2a),(4ac-b²)/(4a) ]
x=-b/(2a)
=(1/2)/(2×1/3)
=3/4
对称轴为 x=3/4
(4ac-b²)/(4a)
=[4×1/3×(-2)-(-1/2)²]/(4×1/3)
=(-8/3-1/4)/(4/3)
=(-35/12)×3/4
=-35/16
顶点坐标为( 3/4,-35/16)