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 slightly better:
E = ( m 2
c 4
+
c 2
p 2
)
1/2
.
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.