1/2AB=1/2(a)(r) + 1/2(b)(r) + 1/2(c)(r)

president thomas jefferson commissioned the expedition shortly after the louisiana purchase in 1803 to explore and to map the newly acquired territory, to find a practical route across the western half of the continent, and to establish an american presence in this territory before britain and other european powers

not sure might be he acquired the entire oregon territory from great britain