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Discussion: All Tools in Math 7
Topic: teaching about scale


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Subject:   RE: scaling on coordinate plane
Author: Craig
Date: Jun 15 2005
This is a real problem, not just at 7th grade level... my Algebra 1 students
(OK, some are 7th graders) and even my seniors in Statistics struggle with it.
Technology is probably the worst approach to solving the problem (that cursed
"ZoomFit" on the TI-83 should be hardwired to shock any student who tries to
use it)!

If they're graphing functions, as opposed to data, then I suggest that once
students have decided on names and units for the axis, they should choose some
realistic "small" values and realistic "large" values for the horizontal
variable, and compute corresponding values for the vertical variable.  Depending
on their maturity, they should adjust scales to include "a little bit" beyond
the chosen and calculated values (or 10-20% beyond for more mature students).
Of course, you need to decide whether you will require axes to intersect at the
origin.

This method won't work well if the function is not monotonic, but it will give a
start.  I think it is important to be "grounded" by having units associated with
each axis, and by choosing "realistic" input values (though you might have to
guide them into what "realistic" might mean in some settings).

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