The square of x is the square of x (symbols can't be typed, they can only be explained in words). The so-called "descending order" means that x is used to represent the square of X.

If it is junior high school, just use "descending order" (descending order, such as x+x2 (the square of x) +2, and then x2+x+2).

In high school, I only knew that trigonometric functions have "reduced order", such as the square of sin x = (1-cos 2x)/2.