Apple iWork '09 - Manual (Page 15)

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This chapter explains how to perform calculations in table
cells by using formulas.
The Elements of Formulas
A formula performs a calculation and displays the result in the cell where you place
the formula. A cell containing a formula is referred to as a formula cell.
For example, in the bottom cell of a column you can insert a formula that sums the
numbers in all the cells above it. If any of the values in the cells above the formula cell
change, the sum displayed in the formula cell updates automatically.
A formula performs calculations using specific values you provide. The values can
be numbers or text (constants) you type into the formula. Or they can be values that
reside in table cells you identify in the formula by using cell references. Formulas use
operators and functions to perform calculations using the values you provide:
 Operators are symbols that initiate arithmetic, comparison, or string operations. You
use the symbols in formulas to indicate the operation you want to use. For example,
the symbol + adds values, and the symbol = compares two values to determine
whether they’re equal.
=A2 + 16: A formula that uses an operator to add two values.
=: Always precedes a formula.
A2: A cell reference. A2 refers to the second cell in the first column.
+: An arithmetic operator that adds the value that precedes it with the value that
follows it.
16: A numeric constant.
 Functions are predefined, named operations, such as SUM and AVERAGE. To use a
function, you enter its name and, in parentheses following the name, you provide
the arguments the function needs. Arguments specify the values the function will
use when it performs its operations.
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Using Formulas in Tables