Assume That the Demand for an Electric Toothbrush (X) Is $$Q D _ { X } = 1000 - 10 P _ { X } - 5 P _ { Y } + 2 P _ { Z }$$

Essay

Assume that the demand for an electric toothbrush (X) is represented by the following equation:
$$Q D _ { X } = 1000 - 10 P _ { X } - 5 P _ { Y } + 2 P _ { Z }$$ Which of the products Y and Z is a substitute and which of them is a complement to an electric toothbrush? Give examples for goods Y and Z.