The method of polynomial simplification and evaluation is: simplification first, then evaluation. Polynomial simplification involves many additions and subtractions of algebraic expressions: its essence is to remove brackets and merge similar items, and its general steps are: (1) If there are brackets, remove them first; (2) If there are similar items, merge them again. Note: the final result of algebraic expression addition and subtraction cannot contain similar items, that is, it must be merged until it can no longer be merged. Addition and subtraction of algebraic expressions mean merging similar terms. Add and subtract similar items, and pull down those that cannot be calculated. When merging similar items, we should pay attention to the following three points: ① Only by mastering the concept of similar items can we distinguish similar items and accurately grasp two criteria for judging similar items: letters and letter indexes; (2) The definition of merging similar terms means merging similar terms in polynomials into one term. After merging similar terms, the number of terms in the formula will be reduced, thus simplifying the polynomial; (3) "Merging" refers to adding the coefficients of similar items, and the obtained results are used as new coefficients, and the letters and letter indexes of similar items should remain unchanged.