问题
解答题
用配方法把函数y=1-4x-2x2化成y=a(x+m)2+k的形式,并指出它的图象的开口方向、顶点坐标和对称轴.
答案
y=1-4x-2x2,
=-2(x2+2x+1)+2+1,
=-2(x+1)2+3,
所以,∵a=-2<0,
∴它的图象的开口方向向下,
顶点坐标为(-1,3),
对称轴为直线x=-1.
用配方法把函数y=1-4x-2x2化成y=a(x+m)2+k的形式,并指出它的图象的开口方向、顶点坐标和对称轴.
y=1-4x-2x2,
=-2(x2+2x+1)+2+1,
=-2(x+1)2+3,
所以,∵a=-2<0,
∴它的图象的开口方向向下,
顶点坐标为(-1,3),
对称轴为直线x=-1.
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