Two polio vaccines are used throughout the world to combat polio. The first was invented by Jonas Salk, and first tested in 1952 and announced to the world by Salk on March 26, 1953. It consists of an injected dose of killed polio virus. Albert Sabin[?] produced a cheaper and more effective oral polio vaccine in 1962.
... The two solutions are complex conjugates of each other. (In this case, the parabola does not intersect the x-axis at all.)
Note that when computing roots ...