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Chapter 1: Variables, Function
Patterns, and Graphs
1.1
Using Variables
Variables
• A symbol, usually a letter, that represents an
unknown quantity
Expression vs Equation
• Algebraic expression: a mathematical phrase that
can include numbers, variables, and operation
symbols
– Does not have an equals sign
• Equation: a statement that two expressions are
equal to each other
– Has an equals sign
Example 1
• Write an algebraic expression for each phrase:
• Seven more than n
• The difference of n and 7
• The product of seven and n
• The quotient of n and seven
Example 2
• Define a variable and write an algebraic expression
for each phrase:
• Two times a number plus five
• Seven less than three times a number
Example 2a
• Define a variable and write an algebraic expression
for each phrase:
• Nine less than a number
• The sum of twice a number and 31
Equations
• Mathematical sentence that uses an equal sign
• If true, then the expressions on either side
represent the same value
• If there’s one or more variables, the equation is an
open sentence
• “is” suggests an equal sign
Example 3
• Track One Media sells all CDs for $12 each. Which
equation best represents the cost c of a given
number n of CDs?
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•
•
•
12 + c = n
n + 12 = c
12c = n
c = 12n
Example 3a
• Suppose the manager at Track One Media
uses the equation c = 10.99n. What could this
mean?
Homework
• P. 6
• 2-40 even