As the saying goes, "Birds of a feather flock together, and people are divided into groups". It means that the same kind of things can be gathered together. Of course, different types of things can't be gathered at will. For example, clean the room, put books on the bookshelf, put clothes in the closet, put dishes in the cupboard, ... Don't put bowls in the closet, pile clothes on the bookshelf, ... visit the zoo, tigers and tigers are in one cage, pandas and pandas are in another cage. You can't keep the panda and the tiger together, or the panda will be eaten by the tiger. This is "birds of a feather flock together".

In mathematics, this idea of similar sets is often used.

Take the name number as an example. The units in 3 yuan and 2 yuan are all yuan, which can be added together and equal to 5 yuan. 3 yuan 8 and 2 yuan 3 can also be added, but it should be noted that RMB can only be Canadian dollars, RMB can only be added, and RMB can't be added. The answer should be 6 yuan L. If different names can be replaced by the same number, they must be replaced by the same number before adding; If it cannot be converted into a number with the same name, it cannot be added. For example, 3 kilograms and 6 yuan represent different quantities, and these two units can't be replaced by the same one anyway, so they can be added together.

Why emphasize "number alignment" in integer addition and subtraction? Because after the numbers are aligned, the units of the numbers on the same number are the same, and they can be added or subtracted. Similarly, decimal addition and subtraction emphasizes "decimal point alignment", because once the decimal point is aligned, the digits of the integer part and the decimal part are also aligned, so you can add and subtract.

Look at the addition and subtraction of fractions. Denominators have the same decimal units and can be added or subtracted directly; Fractions with different denominators have different units, so they cannot be added or subtracted directly. They must be divided first. The essence of the total score is to change the scores of different units into the scores of the same unit. Fractions can be added and subtracted only when the units are the same.

Now, let's look at the problem of merging similar items, which is the basis of algebraic addition and subtraction. When energy is added, the unit can be regarded as. Can be understood as three, can be understood as five, together should be eight, namely

.

Similarly, 6ab MINUS 4ab can be regarded as ab, and 6 ab MINUS 4 ab can get 2 AB, that is

6ab-4ab=2ab .

Therefore, for the addition and subtraction of polynomials, similar items can be merged, not to say that similar items cannot be merged. In a word, birds of a feather flock together, so we should pay attention to the characteristic of "the same kind" when adding and subtracting algebra.