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俄罗斯的小说《投入大海的怀抱》中的一位主角曾经有过这样的怀疑：当他环球旅行的时候,究竟身体的哪一部分走了更多的路——是头顶呢还是脚底呢?这个问题可以演变成如下数学问题：假设你在赤道上绕了地球一圈,那么,你的头顶要比脚底多跑多少路?有同学可能会想,这要知道地球半径和人的身高才行.人的身高可量,假设是17米,地球半径你能记住更好,不记得也没关系,就设为R米吧,则有人的脚底所走的路程为2πR米.人的头顶所走的路程为2π(R＋17)米.因此,头顶和脚底所走路程之差为2π(R＋17)－2πR=2π×17≈107(米).问题已解决.若就此罢手,则十分可惜.因为进一步思考,我们还可以总结出有趣且有用的两点：1计算过程中,地球半径R自行消去,也就是说R只起了一个辅助作用,这种解题方法就叫做辅助未知数法,或叫参数法.
One of the protagonists in the Russian novel “Into the Sea” has had this suspicion: When he traveled around the globe, which part of the body took more roads - is it the top of the head or the bottom of the foot? This problem It can be transformed into the following mathematical problem: Suppose you circle the Earth on the equator, then how much more is your head to run than on the soles of your feet? Some students may think that it is necessary to know the radius of the earth and the height of the person. The height is measurable, assuming it is 1.7m. You can remember the earth’s radius better. If you don’t remember it, it’s okay. Let’s set it as Rm. Then someone’s foot will walk 2πR meters away. The distance is 2π(R+17) meters. Therefore, the distance between the head and sole is 2π(R+17)-2πR=2π×17≈107(m). The problem has been solved. If so, It’s a pity to stop. Because of further thinking, we can also sum up two interesting and useful points: 1. In the calculation process, the radius of the Earth R disappears on its own, which means that R only plays an auxiliary role. This kind of problem solving method It is called auxiliary unknown method, or parameter method.