Final answer:
The feature that increases the predictive power of the regression equation is the closeness of the data points to the regression line.
Step-by-step explanation:
The feature that increases the predictive power of the regression equation is how close the data points are to the regression, or best fit, line. When the data points are closer to the regression line, it indicates a stronger linear relationship between the variables and a more accurate prediction can be made. On the other hand, the mathematical function for the regression line, the slope of the regression line, and the value of the independent variable do not directly increase the predictive power of the regression equation.