CHAPTER 2 Overcoming Mathophobia: Reading and Understanding Mathematical Expressions 19
Addition and subtraction
Addition and subtraction are always indicated by the + and – symbols, respec-
tively, placed between two numbers or variables. Compared to the plus sign, the
minus sign can be tricky when it comes to interpreting it in a formula.»
» A minus sign placed immediately before a number indicates a negative
quantity. For example, –5° indicates five degrees below 0, and –5 kg indicates
a weight loss of 5 kilograms.»
» A minus sign placed immediately before a variable tells you to reverse the
sign of the value of the variable. Therefore, –x means that if x is positive, you
should now make it negative. But it also means that if x is negative, make it
positive (so, if x was –5 kg, then –x would be 5 kg). Used this way, the minus
sign is referred to as a unary operator because it’s acting on only one variable.
Multiplication
The word term is generic for an individual item or element in a formula. Multipli-
cation of terms is indicated in several ways, as shown in Table 2-1.
You can put terms right next to each other to imply multiplication only when it’s
perfectly clear from the context of the formula that the authors are using only
single-letter variable names (like x and y), and that they’re describing calcula-
tions where it makes sense to multiply those variables together. In other words,
you can’t put numeric terms right after one another to imply multiplication,
TABLE 2-1
Multiplication Options
What It Is
Example
Where It’s Used
Asterisk
2
5
*
Plain text formulas, but almost never in
typeset formulas
Cross
2
5
Typeset formula, between two variables or
two constants being multiplied together
Raised dot
2 5
Typeset formula
Term is immediately in front of a
parenthesized expression
2 5
3
16
Typeset formula
Brackets and curly braces
2 6
5
3
2
20
/
Typeset formula containing “nested”
parentheses
Two or more terms running
together
2
2
r
r
versus
In typeset formulas only