追擊相遇問題

列一元一次方程解應(yīng)用題（復(fù)習(xí)課）教學(xué)目標(biāo)：1、會(huì)借助示意圖、表格分析題意，尋找相等關(guān)系；2、通過列方程解應(yīng)用題，培養(yǎng)學(xué)生分析問題、解決問題的能力；列方程解應(yīng)用題步驟：5、檢查所得的值是否正確和符合實(shí)際情形，并寫出答案（包括單位名稱）。1、弄清題意，用字母（如X）表示問題里的未知數(shù)；2、分析題意，找出相等關(guān)系（可借助于示意圖、表格）；3、根據(jù)相等關(guān)系，列出需要的代數(shù)式，從而列出方程；（注意：左右兩邊單位統(tǒng)一，已知條件都要用上）4、解這個(gè)方程，求出未知數(shù)的值；填空：1、甲乙兩車從相距108千米處同時(shí)出發(fā)，相向而行，已知甲車速度為19千米/時(shí)，乙車速度為17千米/時(shí)———小時(shí)后，兩車在相遇前相距36千米。22、（接上題）又過了———小時(shí)，兩車相遇后相距36千米。由相遇前相距36千米，到相遇后相距36千米，兩車共行駛———千米。23、若甲乙兩車從相距108千米A、B處同時(shí)相向而行，已知甲車速度為19千米/時(shí)，乙車速度為17千米/時(shí)，到達(dá)B、A后立即返回原處，兩車第一次相遇時(shí)間為———小時(shí)，從第一次相遇到第二次相遇的時(shí)間為———小時(shí)。6372例1：甲、乙兩車從A、B兩地于上午8點(diǎn)鐘同時(shí)出發(fā)，相向而行，已知甲的速度比乙快2千米/時(shí)，到上午10時(shí)兩車還相距36千米，又過了兩小時(shí)后，兩車又相距36千米。1、求甲乙兩地間的距離與兩車的速度；2、若甲乙兩車分別從A、B兩地同時(shí)相向而行，到B、A兩地后立即返回，求兩車第一次相遇和第二次相遇所走的時(shí)間是多少？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小時(shí)的路程(S1)乙行2小時(shí)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小時(shí)的路程乙行2小時(shí)的路程36千米36千米AB甲行2小時(shí)的路程(S1)乙行2小時(shí)的路程(s2)甲乙36千米甲乙

解：⑴設(shè)乙車速度為X千米/時(shí)，則甲車速度為（X+2）

千米/時(shí)。依題意列方程：2X+2（X+2）=72

解得X=17，X+2=19，A、B兩地距離為：72+36=108答：A、B兩地距離是108千米，甲車速度為19千米/時(shí)，乙車速度為17千米/時(shí)。相等關(guān)系：前2小時(shí)所行駛的路程=后2小時(shí)所行駛的路程分析：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→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→→←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←←