+/-means positive or negative. There is a horizontal line below. This symbol means that both positive and negative symbols have symbols. () is a mathematical symbol, which is used to express the accuracy of approximation, or the abbreviation of quantity with two possibilities. "Add or subtract" means positive or negative, and symbols can be used to represent the positive or negative of rational numbers, or to add and subtract logarithms in four operations. Symbol is not a single concept in middle school physics. Some symbols are equivalent to rational numbers in mathematics, while others are used to express the nature and direction of physical quantities. The situation is more complicated.