1. In mathematics, a stands for the absolute value of a. In mathematics, a stands for letters and can be used instead of numbers.

2. If a and 1 are reciprocal, then a=- 1,-1= 1. The absolute value is the distance from a point corresponding to a number on the exponential axis to the origin, which is represented by "a". B-a or a-b represents the distance between the point representing a and the point representing b on the number axis.