Final answer:
Lewis and Clark were appointed by Thomas Jefferson to explore and map the Louisiana Territory as part of the Louisiana Purchase. Their objectives were to find a route to the Pacific Coast, map the territory, and establish trade with tribes in the west.
Step-by-step explanation:
Lewis and Clark's role in the Louisiana Purchase was that they were appointed by Thomas Jefferson to lead an expedition to explore and map the newly acquired Louisiana Territory. Their main objectives were to find an all-water route from the Missouri River to the Pacific Coast, map the territory they passed through, and establish trade routes with the western tribes. They did not make the deal to purchase the territory, but their exploration helped to legitimize American claims to the land and secure American influence and power in the west.