Final answer:
The studies of cosmic background radiation have uncovered variations in temperature, confirming the Big Bang theory and providing evidence for the inflationary model of the universe's expansion.
Step-by-step explanation:
The three missions studying cosmic background radiation have uncovered significant discoveries relating to the origins and evolution of the universe. They have found variations in the temperature of the cosmic microwave background radiation, which indicates small differences in density. These variations are the imprints of the tiny fluctuations in the density of the early universe. Additionally, these missions have provided confirmation of the Big Bang theory and its predictions, as well as evidence supporting the inflationary model of the universe's rapid expansion shortly after the Big Bang. This understanding comes from the fact that while we expected to see temperature variations in the cosmic microwave background radiation as remnants of the Big Bang's fireball, the observed temperature variations were even smaller than initially expected, suggesting a very homogeneous and isotropic early universe. The inflation theory helps to explain why the cosmic microwave background has nearly the same temperature in all directions and why the density of the universe is so close to the critical density.