追击相遇问题

列一元一次方程解应用题（复习课）教学目标：1、会借助示意图、表格分析题意，寻找相等关系；2、通过列方程解应用题，培养学生分析问题、解决问题的能力；列方程解应用题步骤：5、检查所得的值是否正确和符合实际情形，并写出答案（包括单位名称）。1、弄清题意，用字母（如X）表示问题里的未知数；2、分析题意，找出相等关系（可借助于示意图、表格）；3、根据相等关系，列出需要的代数式，从而列出方程；（注意：左右两边单位统一，已知条件都要用上）4、解这个方程，求出未知数的值；填空：1、甲乙两车从相距108千米处同时出发，相向而行，已知甲车速度为19千米/时，乙车速度为17千米/时———小时后，两车在相遇前相距36千米。22、（接上题）又过了———小时，两车相遇后相距36千米。由相遇前相距36千米，到相遇后相距36千米，两车共行驶———千米。23、若甲乙两车从相距108千米A、B处同时相向而行，已知甲车速度为19千米/时，乙车速度为17千米/时，到达B、A后立即返回原处，两车第一次相遇时间为———小时，从第一次相遇到第二次相遇的时间为———小时。6372例1：甲、乙两车从A、B两地于上午8点钟同时出发，相向而行，已知甲的速度比乙快2千米/时，到上午10时两车还相距36千米，又过了两小时后，两车又相距36千米。1、求甲乙两地间的距离与两车的速度；2、若甲乙两车分别从A、B两地同时相向而行，到B、A两地后立即返回，求两车第一次相遇和第二次相遇所走的时间是多少？分析：甲乙→←分析：甲乙→→←←分析：甲乙→→→←←←分析：甲乙→→→→←←←←分析：甲乙→→→→→←←←←分析：甲乙→→→→→→←←←←←分析：甲乙→→→→→→→←←←←←←分析：甲乙→→→→→→→→←←←←←←←分析：甲乙→→→→→→→→→←←←←←←←分析：甲乙→→→→→→→→→→←←←←←←←←分析：甲乙→→→→→→→→→→→←←←←←←←←←分析：甲乙→→→→→→→→→→→→←←←←←←←←←←分析：甲乙→→→→→→→→→→→→←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→←←←←←←←←←←←←36千米AB甲乙甲行2小时的路程(S1)乙行2小时的路程(s2)甲乙36千米分析：甲乙→→→→→→→→→→→→→→←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←AB甲行2小时的路程乙行2小时的路程36千米36千米AB甲行2小时的路程(S1)乙行2小时的路程(s2)甲乙36千米甲乙

解：⑴设乙车速度为X千米/时，则甲车速度为（X+2）

千米/时。依题意列方程：2X+2（X+2）=72

解得X=17，X+2=19，A、B两地距离为：72+36=108答：A、B两地距离是108千米，甲车速度为19千米/时，乙车速度为17千米/时。相等关系：前2小时所行驶的路程=后2小时所行驶的路程分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→分析：甲乙←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←分析：甲乙←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←分析：甲乙←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→←←←←←←←←←←←←←←←←←←←←分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←→→→→→→→→→→→分析：甲乙→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←