Step 1: suppose (1+x)/x = y, and convert it into x = 1/(y- 1).

Step 2: Knowing the expression on the right side of the function, convert all X into Y expression, and replace X with 1/(y- 1).

It seems that the expression on the right side of X is Y after expression conversion. It means "with ..."

Step 3: the expression of function side length f (y) = y, that is, f(y) = y? -Yeah.

The expression of f(y) = y here is the same as the expression of f(x) = x, but the sign of the variable is changed.

f(x) = x？ [Add to nouns in French etymology ending in -u to form plural]