Scientific English as a Foreign Language
Lesson of July 17, 1998
Editing Equations

A common mistake is to treat equations differently from text. You should think of your equations as sentences. Isn't "A equals B" the same as "A = B"? Therefore you should punctuate an equation as you would a sentence. The following equation is a complete thought.

A + B = C.

A sentence needs a period. If you want to specify what A, B, and C are, then you would punctuate differently.

A + B = C,

where A is the number of adult gnus, B is their offspring, and C is the total population of the herd. Notice that I did not indent the word "where", because it is not the beginning of a new paragraph. If I change subjects, as I shall now do, I would make the subsequent sentence a new paragraph, and consequently indent. Given that A is the number of adult gnus, B is their offspring, and C is the total population of the herd, we arrive at

A + B = C.

Isn't it easy, once you think about it? There's no reason that an equation can't end with an exclamation point or a question mark. If you are astonished that gnu populations are growing so rapidly, you would write

A + B = C  !!

(Notice that I put space between "C" and the first exclamation point, and used two, not one, exclamation points, in order to avoid confusion with the symbol "!" for factorials.) And if you were learning math, you might ask if

A + B = C?

In the beginning was a black bomb
That blew apart. A blinding smoke
Kept growing, growing

To a tropical fog, intolerably bright.
From this, white whorls of moonshine mist
Distilled, and then distilled

To petal-eddies on a dark pool.
And now they spin in clusters
Farther and farther apart

Like shining catkins, twisted into spools.
All forms, all time, all complexity,
From the first snowdrop to muffins and tea

Lay in that round black bomb
And will return there
When the hot afternoon is done.

-E. Larrissy

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Created July 17, 1998, by Nancy Burnham and Fred Hutson.