30．已知:如图14.抛物线与轴交于点.点.与直线相交于点.点.直线与轴交于点． (1)写出直线的解析式． (2)求的面积． (3)若点在线段上以每秒1个单位长度的速度从向运动(不与重合).同时.点在射线上以每秒2个单位长度的速度从向运动．设运动时间为秒.请写出的面积与的函数关系式.并求出点运动多少时间时.的面积最大.最大面积是多少? 解:(1)在中.令 . .··············································· 1分又点在上的解析式为·············································································· 2分 (2)由.得 ···················································· 4分 . .······························································································· 5分 ························································································· 6分 (3)过点作于点 ······························································································· 7分 ·········································································································· 8分由直线可得: 在中...则 .······················································································· 9分 ···················································································· 10分 ····························································································· 11分此抛物线开口向下.当时. 当点运动2秒时.的面积达到最大.最大为．···························· 12分【查看更多】

题目列表(包括答案和解析)

27、在一次数学知识竞赛中，竞赛题共30题．规定：答对一道题得4分，不答或答错一道题倒扣2分，得分不低于60分者得奖．得奖者至少应答对

道题．

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一次数学竞赛共30题，每题给出4个答案，期中只有一个正确，要求学生将正确答案选出来，每道题选对得4分，不选或选错倒扣1分．
（1）小明在这次竞赛中得了80分，问他选对了多少题？
（2）这时，小高过来对小明说，自己在这次竞赛中得了92分，请问小高的话可信吗？说明理由．

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6、下列各数中，属于科学记数法的是（　　）

A、308×10⁸

B、0.308×10¹¹

C、3.08×10¹⁰

D、30.8×10⁹

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