The total revenue curve reaches its maximum at a quantity of air conditioners per year. at this point, the slope of the total revenue curve is

Equal to zero

Explanation: Slope is a number that describes the steepness of a line or curve. At the maximum point, the total revenue curve becomes flat. At this point the slop of the curve given by the rate of change in the curve is equal to zero. it is neither increasing nor decreasing at the maximum point.  

Slope is calculated as,  

Total revenue curve is the relation between total revenue and quantity. At the maximum, change in total revenue is zero so the slope will also be zero.

= 0

answerindustrial revolution;

answertaxable income;