Ask an experienced primary school teacher, is x=x an equation? Is x=x+ 1 an equation? Is x+y=x+y an equation? Is x= 100 an equation? Is x+7=x+7 an equation?

Generally speaking, judging whether an equation is an equation is usually sorted out first. If sorted out (that is, simplified), it is still an unknown equation.

Then this equation is the equation. Let's look at these examples:

(1) "x = x": Obviously, after sorting, this equation becomes: 0=0. Therefore, it is just an identity, not an equation;

(2) "x = x+1":After sorting out, this equation becomes: 0= 1. Obviously, it is not an equation. If you really encounter this problem, you will know that it is a wrong question;

(3) "x+y = x+y": it is the same as (1) after sorting, and becomes 0=0. This is not an equation, but an identity;

(4) "x =100": obviously, it does not need to be sorted out, which completely conforms to the definition of the equation. So "x= 100" is an equation;

(5) "x+y = x+y": it also becomes: 0=0 after sorting. So, this is not an equation, but an identity.