题干

给出定义:设一条直线与一条抛物线只有一个公共点,且这条直线与这条抛物线的对称轴不平行,就称直线与抛物线相切,这条直线是抛物线的切线.有下列命题:

①直线y=0是抛物线y=

1
4
x2的切线;

②直线x=﹣2与抛物线y=

1
4
x2 相切于点(﹣2,1);

③若直线y=x+b与抛物线y=

1
4
x2相切,则相切于点(2,1);

④若直线y=kx﹣2与抛物线y=

1
4
x2相切,则实数k= 2

其中正确命题的是(   )

A:①②④

B:①③

C:②③

D:①③④

上一题 下一题 0.0难度 选择题 更新时间:2017-05-17 08:48:18

答案(点此获取答案解析)

B

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