Children in large classes can effectively learn the knowledge of the decomposition and composition of numbers in primary schools. The decomposition and synthesis of numbers are arranged in the large class textbooks of kindergartens, in which the first semester is the decomposition and synthesis of numbers within 5.

Cultivate the interest and hobby of active exploration, develop children's ability of observation, thinking and hands-on operation, and cultivate children's sense of cooperation. By letting children actually operate, record and explore the decomposition and composition of "5", observe and find out the law of increase and decrease, and perceive the exchange position and invariant relationship between two numbers.

Formula method

If a polynomial satisfies the structural characteristics of a special formula, it can be decomposed by a set of formulas. Therefore, you need to be familiar with some commonly used formulas. In addition to the basic formulas in textbooks, some basic formulas that often appear in math competitions are summarized as follows.

Answer? -B? =(a+b)(a-b)

Answer? 2ab+b？ =(a b)？

Answer? +b？ =(a+b)(a？ -ab+b？ )

Answer? -B? =(a-b)(a？ +ab+b？ )