Refer to the quadratic model used for Exercises 1–9. Suppose that y is the profit for some business and x is the amount of capital invested, and you know that the rate of increase in profit for a unit increase in capital invested can only decrease as x increases. You want to know whether the data provide sufficient evidence to indicate a decreasing rate of increase in profit as the amount of capital invested increases. Use this information to answer the questions in Exercises 10.

10. The circumstances described imply a one-tailed statistical test. Why?