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

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解：y=1/3x²-1/2x-2
a=1/3 , b=-1/2 , c=-2，对称轴为x=-b/春余(2a)；顶点坐标为[ -b/扒中滚(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/培谨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)

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