The expression (p1.x/2) + (p2.x/2) is used in the midpoint method for calculating elasticity because it uses a consistent average base, ensuring the same elasticity is achieved regardless of the direction of the price change.
The expression (p1.x/2) + (p2.x/2) is preferred over (p1.x + p2.x)/2 in the midpoint method because it ensures that the same base is used regardless of whether there is a price increase or decrease. This approach results in consistent elasticity calculation between two price points. The midpoint formula effectively handles the percentage change calculation by using the average of initial and final values as the base for both the numerator and denominator, thereby maintaining symmetry in the elasticity measure.
In the context of economics, this method is especially relevant as it provides an unbiased elasticity result which is not affected by the direction of the change in price. By calculating each term separately and then adding them, the expression protects against skewed results that can occur due to significant differences in the starting and ending values.