Development and integration of mathematics
First of all, we must clarify the concept. Items with the same letters and the same index are called similar items. Merging similar terms in polynomials into one term is called merging similar terms. Metaphorically speaking. Two chickens can only be combined with three chickens to make five chickens. It can't blend with three ducks. In addition, it should be noted that the index of letters is the same before merging.