Variable Expressions

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Key Questions

  • Variables are symbols representing some changing quantities.


    I hope that this was helpful.

  • Variable expressions are expressions that involve variables, which are symbols that represent changing quantities. (See http://socratic.org/questions/what-are-variables for reference). The value of the expression will change as the value of the variable changes.

    For example, let's say with have the equation #x + 5#

    When #x = 1 #, then #x + 5 = 6#

    When #x = 2 # then #x+5 = 7#

    Hope that was helpful.

  • To write variable expressions on Socratic, simply place hash tags around the expression when typing it:

    [hash tag] x + 1 [hash tag] = #x +1#

    [hash tag] (x-1)/(x+1) [hash tag] = #(x-1)/(x+1)#

    Hope that was helpful.

  • To evaluate a variable expression means to find the value of the expression when the variable is (or variables are) replaced by a number (or numbers).

    Here is a variable expression: #3x+7#.

    To evaluate this expression when #x = 2# mean to substitute #2# in place of #x#, and find the number (the value). [see note below]

    #3(2)+7 = 6+7 = 13#.

    When #x=2#, the expression has a value of `#13#.

    If we evaluate the same expression when #x=10#, we get:

    #3(10)+7 = 30+7 =37#.

    Here's a variable expression with two variables : #3x-2y#

    In order to evaluate this expression, we'll need values (numbers) for both #x# and #y#.

    Evaluate the expression #3x-2y# when #x=4# and #y=5#

    #3(4)-2(5) = 12 - 10 = 2#

    If we change the values to #x=5# and #y=4#, we get
    #3(5)-2(4) = 15 - 8 =7#.

    Note:

    To avoid saying exactly the same thing over and over, we use the following to mean the same thing:

    evaluate the expression when #x = 2#
    evaluate the expression for #x = 2#
    evaluate the expression at #x = 2#
    evaluate the expression assuming #x = 2#
    evaluate the expression if #x = 2#

    Also

    If there is only one variable in an expression, we don't always need to mention it:
    evaluate the expression for #2#
    evaluate the expression at #2#

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