Introduce all important concepts and their symbols before the equation appears. Note: symbols are in italics):
[Example] The centrality of the velocity of light c in special relativity is evidenced by the energy E of a mass m moving with momentum p: E = (m2c4+ c2p2)1/2 or as dissplayed equations:
Consider defining resistance R in terms of voltage V driving a current.
In text the preferred form is R = V/I.
Only in display equations should the built-up formed be used, e.g.,
Note the equation is part of the sentence and must be punctuated.