新编高中数学课本第二册 (上 )有这样一道练习题 :一段长为ｌｍ的篱笆围成一个一边靠墙的矩形菜园 ,问这个矩形的长、宽各为多少时 ,菜园的面积图 1　解法 1用图最大 ,最大值是多少 ?下面先分析这道题的解法 .解法 1　如图 1,设矩形的宽为ｘｍ ,则其长为 (ｌ - 2ｘ)ｍ ,面积Ｓ The second volume of the new high school mathematics textbook (above) has such a practice: A fence with a length of lm encloses a rectangular vegetable garden on one side of the wall. When asked about the length and width of the rectangle, the area of ​​the vegetable garden is shown in Figure 1. Solve 1 using the map the largest, the maximum value is how? First analyze the problem of this solution. Solution 1 In Figure 1, set the width of the rectangle is xm, then its length is (l - 2x) m, area S