摘要： 解:(1)设药物燃烧阶段函数解析式为.由题意得: ························································································································ 2分 ．此阶段函数解析式为······································································· 3分 (2)设药物燃烧结束后的函数解析式为.由题意得: ·························································································································· 5分 ．此阶段函数解析式为······································································ 6分 (3)当时.得···················································································· 7分 ························································································································· 8分 ·························································································································· 9分 从消毒开始经过50分钟后学生才可回教室．···························································· 10分
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七年级学生参加了社会实践调查活动，到生态果园调查后得到如下信息：今年收获了15吨李子和8吨桃子，要租用甲、乙两种货车共6辆，及时运往外地，经询问，甲种货车可装李子4吨和桃子1吨，乙种货车可装李子1吨和桃子3吨．根据同学们带回的信息，试探究以下问题：
（1）共有几种租车方案？
（2）经咨询运输公司，甲种货车每辆需付运费1000元，乙种货车每辆需付运费700元，试帮助选出最佳方案，并求出此方案运费是多少．
请同学们补充完成下列部分解题过程：
（1）解：
①若设租用甲车x辆，则租用乙车
②由题意可知：甲车一共可装
请列出不等式
③甲车一共可装
请列出不等式
④请列出不等式组，并求出满足不等组的整数解，写出相应的方案
（2）解：
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（1）共有几种租车方案？
（2）经咨询运输公司，甲种货车每辆需付运费1000元，乙种货车每辆需付运费700元，试帮助选出最佳方案，并求出此方案运费是多少．
请同学们补充完成下列部分解题过程：
（1）解：
①若设租用甲车x辆，则租用乙车
（6-x）
（6-x）
辆，②由题意可知：甲车一共可装
x
x
吨桃子，乙车一共可装3（6-x）
3（6-x）
吨桃子，则甲，乙两种车一共可装x+3（6-x）
x+3（6-x）
吨桃子．（用含有x的代数式表示）请列出不等式
x+3（6-x）≥8
x+3（6-x）≥8
③甲车一共可装
4x
4x
吨李子，乙车一共可装（6-x）
（6-x）
吨李子，则甲，乙两种车一共可装4x+（6-x）
4x+（6-x）
吨李子．（用含有x的代数式表示）请列出不等式
4x+（6-x）≥15
4x+（6-x）≥15
④请列出不等式组，并求出满足不等组的整数解，写出相应的方案
（2）解：
,若设
,则原方程化为关于
的整式方程是
B、
D、
，设
，那么原方程可化为 ．