题干

在平面直角坐标系xOy中,抛物线y=x2+bx+c与x轴交于A、B两点(点A在点B的左侧),点B的坐标为3,0,与y轴交于点C0,3,顶点为D。

(1)求抛物线的解析式及顶点D坐标;
(2)联结AC、BC,求∠ACB的正切值;
上一题 下一题 0.0难度 选择题 更新时间:2010-06-24 09:55:30

答案(点此获取答案解析)

(1)∵抛物线过点B(3,0),点C(0,3),
32+3b+c=0

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    The researchers created a long-termstudy in which they invited families in 16 school districts in central Pennsylvania to participate. In each family, a teenager, a younger sibling, their mother and their father were interviewed at home and then asked about their activities and self-worth five times over a period of seven years.

    The study authors were surprised to discover that when fathers spent more time alone with their teenagers, the kids reported they felt better about themselves. Something about the father's role in the family seemed to improve self-esteem among the teenagers in the study, said study author Susan McHale, a professor of human development at Pennsylvania State University.

  “Time spent with Dad often involves joking, teasing and other playful interactions. Fathers, as compared to mothers, were more involved in leisure activities and had more friend-like interactions with their children, which is crucial for youth social development,” the study showed.

    But Marta Flaum, a psychologist in Chappaqua , New York, said, “How these findings reflect the real world is areal question. The sample in the study is so small and so unrepresentative of more families in the country today that I'm not sure how much we cangeneralizing from it. In my community, in Westchester County, I don't see parents and teenagers spending much time together at all. Parents are often working so hard and have less time to be together with their kids.”

    However, Flaum encourages parents to make time for their kids no matter how much work they have to do. “Research like this reminds us of how important it is. The time we have with themis so short, ” she said.