············································· 1分 ?A(?2，0)，B(2，0) ·又
点B在y??3x?b上 43?0???b
23b?
233······································································· 2分 ?BC的解析式为y??x? ·
4232?y??x?3?x1??1???4（2）由?，得?9
33y1??y??x???4??429???C??1，?，B(2，0)
4???x2?2 ·················································· 4分 ?y?0?29 ······················································································· 5分 4199················································································· 6分 ?S△ABC??4?? ·
242（3）过点N作NP?MB于点P EO?MB ?NP∥EO
······················································································ 7分 ?△BNP∽△BEO ·
BNNP ································································································· 8分 ??BEEO?AB?4，CD?由直线y??33?3?x?可得：E?0，? 42?2??在△BEO中，BO?2，EO?35，则BE? 2262tNP，?NP?t ················································································ 9分 ?5352216?S?t(4?t)
25312S??t2?t(0?t?4) ············································································· 10分
55312S??(t?2)2? ····················································································· 11分
5512此抛物线开口向下，?当t?2时，S最大?
5??当点M运动2秒时，△MNB的面积达到最大，最大为
12． ···························· 12分 5
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