Graphing Non-f(x) Functions on TI-89 Calculator

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Discussion Overview

The discussion revolves around the capability of the TI-89 calculator to graph equations that are not explicitly defined as functions of the form f(x). Participants explore the potential for graphing implicit functions and the methods available to achieve this.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant inquires about graphing equations like 2x + 3y = 7 and 3y^2 + 2x^2 - 3x + 6 = 0 on the TI-89.
  • Another participant suggests that if y = f(x), one should solve for y, indicating that the TI-89 can handle such transformations.
  • A third participant expresses confidence that only explicit functions can be graphed on the TI-89, reiterating the need to solve for y.
  • One participant mentions that implicit functions can sometimes be graphed using parametric equations, providing the example of a circle defined by x^2 + y^2 = 1.
  • Another participant notes that the TI-89 is programmable and suggests looking for packages or writing custom programs to enhance its graphing capabilities.
  • A later reply indicates that it is possible to write a program to graph implicit equations directly without solving for a variable first.

Areas of Agreement / Disagreement

Participants express differing views on the capabilities of the TI-89 regarding implicit functions. While some suggest that explicit forms are necessary, others propose alternative methods such as parametric graphing or programming solutions. The discussion remains unresolved regarding the best approach to graphing non-explicit functions.

Contextual Notes

Participants mention various methods for graphing, including solving for variables and using parametric equations, but do not reach a consensus on the limitations or capabilities of the TI-89 in handling implicit functions.

jaredmt
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i was wondering if i could graph something like:
2x + 3y = 7
or
3y^2 + 2x^2 -3x +6 = 0

where the function doesn't always start with plain f(x). is it possible to do this on ti 89?
 
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If y=f(x), then solve for y. If you're asking about things that don't have nice explicit forms, eg a 3rd degree polynomial in y, then yes, the TI-89 can solve those for you.
 
Last edited:
Fairly sure you can only graph explicit functions on the TI-89, so like qntty says, you'll have to solve for y (but the TI-89 will do this for you).
 
Sometimes, but not always, you can write implicitely defined functions in terms of explicit functions of a parameter. For example, you can graph x2+ y2= 1, a circle, in parametric graphing mode with x= cos(t), y= sin(t).
 
Now the TI-89 is programmable so you might search the TI site for packages you can upload to expand its capacities or write your own. At worst you can graph the inequality f(x,y) < 0 by iterating over the coordinates on the visible screen and plotting the ones satisfying the inequality. The boundary will then be your curve.
 
Yes, if you want to graph an implicit equation without having to first solve for a variable, you could easily write a program to solve it and input it into Y1.
 

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