There are two ways to handle the fact that 
, the own price elasticity of demand, is negative.
One way is simply to leave it as a negative number. The other way, more
common in introductory courses, is to multiply the expression by -1, reversing the sign to positive, as we have done to the
right. If we do this, the own price elasticity of demand will always be a positive number. Throughout the rest of this
course, we will use to represent own price elasticity of demand, and we will treat
it as a positive number. Keep in mind that this will not be true
for other elasticities. For most elasticities, the sign can change depending on the circumstance.
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