与多项展开式有关的计数问题,灵活性强,思维方法独特,是各类考试的常见题型,用二项式定理或直接用多项式乘法展开求解,有时比较麻烦,若利用组合知识及分类计数原理与分步计数原理,则容易获得问题的解题思路,且方便、直接、易于掌握.1求项数问题例1(x3+x2+x+1)(y2+y+1)(z+1)展开 Counting problems related to polynomial expansion, flexibility, and unique thinking methods are common types of questions in various examinations. Solving with the binomial theorem or using polynomial multiplication directly, it is sometimes cumbersome to use combination knowledge and classification. The counting principle and step-counting principle make it easy to obtain problem-solving ideas, and it is convenient, direct, and easy to grasp. 1 Item Number Problem 1(x3+x2+x+1)(y2+y+1)(z +1) Expand