我们经常碰到这样一些问题:理论上完全能够解决,而实际上运算浩繁,人力不可为.特别是一些解析几何的计算题,常规的方法有时很难奏效.因此数学解题是非常讲究特殊的思想方法的.设而不求,是一种综合的解题思路,在减少运算量、降低运算难度方面,常有意想不到的效果. We often encounter such problems: Theoretically, it is completely possible to solve it. In fact, the operation is voluminous and manpower cannot be used. In particular, some calculation problems of analytical geometry, conventional methods are sometimes difficult to work. Therefore, mathematical problem solving is very special. The design of ideas and methods, rather than seeking, is a comprehensive way of solving problems. It often has unexpected effects in reducing the amount of calculations and reducing the difficulty of calculation.