The absolute value function is a function defined on the set of real numbers, which represents the absolute value of any real number X, namely |x|. The general form of the absolute value function is as follows: f(x)=|x|, where x ∈ r.

The basic knowledge points of absolute value function are:

1. The definition domain of the absolute value function is the real number set r, and the value domain is the positive real number set r;

2. The increase and decrease and parity of the absolute value function: it monotonically increases in its definition domain, so it is increasing function; In addition, its image is symmetrical about Y axis, so it is odd function;

3. Derivative of absolute value function: f'(x)=sgn(x), where sgn(x) is a symbolic function;

4. The coordinate description formula of absolute value function image: f (x) = | x | = (x 2) (1/2).