2009年天津市中考数学试卷及答案(3)

解得b?16，c?16.

2?函数y2的解析式为y2?x?2621256x?16． ····································································· 3分

（Ⅱ）由已知，得AB?，设△ABM的高为h，

?S△ABM?12AB·h?h?1123，即2h?1144.

根据题意，t?T?16162h，

56161144由T?t?56562t?，得?t?114412t??.

当t?2t?1616??时，解得t1?t2?5?125122；

5?122当t?2t??144时，解得t3?，t4?.

?t的值为

5?25?2，，. ······················································································ 6分 1212125（Ⅲ）由已知，得

????b??c，????T????t??T????t??222?b??c，T?t?bt?c.

2??t???b?，

??t???b?，

2???????b??c?????b??c?，化简得??????????b?1??0.

?0?????1，得????0， ?????b?1?0.

有??b?1???0，??b?1???0. 又0?t?1，?t???b?0，t???b?0，

?当0?t≤a时，T≤?≤?；

当??t≤?时，??T≤?；

当??t?1时，????T. ································································································· 10分

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