一、对两道试题的分析与认识试题1登楼梯时规定,每次只能跨上1级或2级台阶,今欲登上10级楼梯,则不同走法的总数为_.分析这是一道2015年北大自招数学试题.正向思维,从第一级开始思考,由于每一次可以跨上1级或2级台阶,过程比较复杂,很难数清楚有多少走法;逆向思考,从最后一级思考,设走上n级楼梯有a_n种方法,则有a_1=1,a_2=2,注意到每一步只能上1级或2级 First, the analysis and understanding of the two questions test questions 1 ascend the stairs, each time only one or two steps across, now want to board 10 steps, then the total number of different ways is _. Analysis of this is A 2015 Peking University self-recruit math test positive thinking, thinking from the first level, because every time you can step on a level or two steps, the process is more complicated, it is difficult to count the number of walking method; reverse thinking, from The last level of thinking, set up on the n-level staircase has a_n kinds of methods, then a_1 = 1, a_2 = 2, noting that each step can only be on the level 1 or 2