Algebraic Expressions
          A combination of operations on letters (variables) 
          and numbers is called an algebraic expression.
                                                    Algebraic Expressions
                                          5 + x        6 • y       3  •  y – 4 + x 
                                                                       •                    •
                                                            4x means 4 • x
                                                                                              •
                                                             4x means 4  x
                                                                           and
                                                                            and
                                                             xy means x • y
                                                                                                 
                                                             xy means x•y
  © 2011 Pearson Prentice Hall. All rights reserved
                                             Martin-Gay,  Prealgebra & Introductory Algebra, 3ed                                                     22
                         Algebraic Expressions
          Replacing a variable in an expression by a 
          number and then finding the value of the 
          expression is called evaluating the 
          expression for the variable.
  © 2011 Pearson Prentice Hall. All rights reserved
                                 Martin-Gay,  Prealgebra & Introductory Algebra, 3ed                         33
        Evaluating Algebraic Expressions
                Evaluate x + y for x = 5 and y = 2.
                Replace x with 5 and y with 2 in x + y.
                                 x + y = (    )  +  (    )
                                                 5              2
                                         = 7
  © 2011 Pearson Prentice Hall. All rights reserved
                                 Martin-Gay,  Prealgebra & Introductory Algebra, 3ed                         44
                                             Equation
          Statements like  5 + 2 = 7 are called equations.
          An equation is of the form expression = expression
          An equation can be labeled as 
                                              Equal sign
                                         x   +   5  =   9
                                    left side              right side
  © 2011 Pearson Prentice Hall. All rights reserved
                                 Martin-Gay,  Prealgebra & Introductory Algebra, 3ed                         55
                                             Solutions
          When an equation contains a variable, 
          deciding which values of the variable make an 
          equation a true statement is called solving an 
          equation for the variable.
          A solution of an equation is a value for the 
          variable that makes an equation a true 
          statement.
  © 2011 Pearson Prentice Hall. All rights reserved
                                 Martin-Gay,  Prealgebra & Introductory Algebra, 3ed                         66