Final answer:
The cross elasticity between tennis racquets and tennis balls is expected to be positive since they are complementary goods that are used together, affecting each other's demand inversely.
Step-by-step explanation:
We would expect the cross elasticity between tennis racquets and tennis balls to be positive. Cross elasticity of demand measures the responsiveness of the demand for a good to a change in the price of another good. In this case, tennis racquets and tennis balls are complementary goods, meaning they are used together. If the price of tennis racquets increases, people are likely to buy fewer racquets, which in turn would lead to a decrease in the demand for tennis balls. Hence, the cross elasticity between them would be positive, as the demand for one good goes up or down, the demand for the complement moves in the opposite direction.