"瞻前顾后"出自《楚辞.离骚》，含义是看看前面，又看看后面。形容考虑或处理事情谨慎周到。

"Look before and after" comes from "Chu Ci, Li Sao". It means looking at the front and looking at the back. Describe or treat things carefully and carefully.

解答数学题时，很多同学只追求"做出来"，有了一个答案便不再深入思考，缺乏"瞻前顾后"的良好习惯，从而忽略了另外的可能性。

In solving math problems, many students only pursue "do it", and there is an answer that will no longer think deeply and lack the good habit of "looking forward to the back", thus ignoring the other possibility.

例题：甲、乙两车同时从A、B两地相向开出，甲车每小时行45千米，乙车每小时行55千米，4小时后两车相距20千米。求A、B两地的距离。

Examples: A, B two vehicles from both A and B at the same time, a car 45 kilometers per hour, B car 55 kilometers per hour, four hours after the two cars 20 kilometers apart. Find the distance between A and B.

分析与解：这是一道比较简单的行程问题，大多数同学可能这样列式计算：（45+55）×4+20=420（千米）。其实很多同学在解题时忽视了另一种情况：如果两车行驶了4小时已经相遇，并且一共又多行了20千米，那么两地的距离就应该是两车4小时所行的路程再减去20千米。因此，还可以这样列式计算：（45+55）×4-20=380（千米）。这道题存在两种可能性所以答案不是唯一的。

Analysis and Solution: This is a relatively simple journey problem, most students may calculate this formula: (45 + 55) X4 + 20 = 420 (km). In fact, many students neglect another situation when they solve the problem: if the two cars have been running for 4 hours, and a total of 20 kilometers, then the distance between the two places should be reduced to 20 kilometers by the two cars and 4 hours. Therefore, it can also be calculated in this way: (45+55) x 4-20=380 (km). There are two possibilities in this question, so the answer is not unique.