"Invariant establishment" means that no matter how the conditions change, it is always established. Let's give a few examples.

1.f(x)=ax？ +bx+ 1, regardless of the value of ab, f(0)= 1 holds;

2.(x- 1)？ +|y-2|=0 holds, find the values of x and y; Because left ≥0 is a constant, it holds if and only if x = 1 and y = 2.