What would be the shape of the demand curve so that the total revenue curve is

(a) a positively sloped straight line passing through the origin?

(b) a horizontal line?

(a) If the total revenue curve is a positively sloped straight line passing through the origin, then the slope of the demand curve will be a horizontal line parallel to the x-axis.

(b) If the total revenue curve is a horizontal line, then the demand curve will be downward sloping.