Equations can be presented in the text as (1) an inline or (2) a separately formatted element. In any case, mathematical symbols should be presented in italic, and the equations should be consecutively numbered. The equation number should be presented in bracket at the right hand side of the equation.
See the example below for the use of an euqation as a seperate text element. The mathematical symbols are explain right after the equation. Also notice the comma after the equations and the fact that “where” is spelled without a capital: the equation together with the explanation is treated as a single sentence.
Common mistakes with equations and symbols are the inconsistent use of mathematical symbols. This often happens because the write takes his/her inspiration from different sources using different symbols. So check that S is always used for the same underlying concept, and that the same underlying concept is always identified by the same symbol.