Only the price elasticity of demand is negative, so you need to add a negative sign in the calculation process; Generally, other elastic calculations do not need to add a negative sign. For example, income elasticity and supply elasticity directly use the ratio of the change rates of the two variables without adding a negative sign in front.

In fact, this is because demand and price change in opposite directions, so there will be a negative decision in elastic calculation, while supply and income change in the same direction as price, so there is no need to artificially add a negative sign in elastic calculation.

brief introduction

In the rational number teaching in the last semester of grade seven, the symbol of rational number is often a problem that puzzles teachers and students. In order to express quantities with opposite meanings, positive and negative numbers are introduced, that is, adding a+sign before the numbers learned in primary school is positive and a-sign is negative.

In physical vectors and their operations, a positive sign indicates that the direction is the same as the specified positive direction, and a negative sign indicates that the direction is opposite to the specified positive direction. It is stipulated that vector operations on the same line can be transformed into algebraic operations with positive and negative signs. The positive and negative symbols in front of physical quantities such as force, acceleration, impulse, momentum and displacement all indicate direction.