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 Subject: Is "variable" confusing to students? Author: Susan Date: May 8 2009
I'm trying to establish the differences among the following three things:

3x + 5

11 = 3x + 5

y = 3x + 5

The first is an algebraic expression containing the "variable" x.  In this case,
the variable x can take on any value.  It “varies”.

The second is an equation of one variable.  We call x a variable but truly it
doesn't vary.  It is just an "unknown".  We can solve for x and determine it
must equal 2.

In the final case, we have two variables and they do 'vary' depending on each
other’s values.

Should we call the x in the second case an “unknown” and not a variable?   I’ve
seen books say, “solve for the unknown”.

I think we confuse students by calling x “variables” in all of these cases when
in case 2, the x does not vary at all.