对一些问题的结论,若其正面情况复杂,而反面情况简单,不妨从结论的反面去思考和探索,得出反面结论后,就容易得到正面的结论。这种从反面进行思考的思维方法常被称为“正难则反”。 例1 求二项式(3~(1/15)x-y)~(15)展开式中 If the conclusions of some problems are complex and the situation on the opposite side is simple, it may be possible to think and explore from the opposite side of the conclusions. After a negative conclusion is drawn, it is easy to get a positive conclusion. This thinking method of thinking from the opposite side is often referred to as “difficulties and opposites.” Example 1 Find the binomial expression (3~(1/15)x-y)~(15) in the expansion